+//===---------------------------------------------------------------------===//
+
+[ALIAS ANALYSIS]
+
+Type based alias analysis:
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705
+
+We should do better analysis of posix_memalign. At the least it should
+no-capture its pointer argument, at best, we should know that the out-value
+result doesn't point to anything (like malloc). One example of this is in
+SingleSource/Benchmarks/Misc/dt.c
+
+//===---------------------------------------------------------------------===//
+
+A/B get pinned to the stack because we turn an if/then into a select instead
+of PRE'ing the load/store. This may be fixable in instcombine:
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37892
+
+struct X { int i; };
+int foo (int x) {
+ struct X a;
+ struct X b;
+ struct X *p;
+ a.i = 1;
+ b.i = 2;
+ if (x)
+ p = &a;
+ else
+ p = &b;
+ return p->i;
+}
+
+//===---------------------------------------------------------------------===//
+
+Interesting missed case because of control flow flattening (should be 2 loads):
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26629
+With: llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as |
+ opt -mem2reg -gvn -instcombine | llvm-dis
+we miss it because we need 1) CRIT EDGE 2) MULTIPLE DIFFERENT
+VALS PRODUCED BY ONE BLOCK OVER DIFFERENT PATHS
+
+//===---------------------------------------------------------------------===//
+
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19633
+We could eliminate the branch condition here, loading from null is undefined:
+
+struct S { int w, x, y, z; };
+struct T { int r; struct S s; };
+void bar (struct S, int);
+void foo (int a, struct T b)
+{
+ struct S *c = 0;
+ if (a)
+ c = &b.s;
+ bar (*c, a);
+}
+
+//===---------------------------------------------------------------------===//
+
+simplifylibcalls should do several optimizations for strspn/strcspn:
+
+strcspn(x, "") -> strlen(x)
+strcspn("", x) -> 0
+strspn("", x) -> 0
+strspn(x, "") -> strlen(x)
+strspn(x, "a") -> strchr(x, 'a')-x
+
+strcspn(x, "a") -> inlined loop for up to 3 letters (similarly for strspn):
+
+size_t __strcspn_c3 (__const char *__s, int __reject1, int __reject2,
+ int __reject3) {
+ register size_t __result = 0;
+ while (__s[__result] != '\0' && __s[__result] != __reject1 &&
+ __s[__result] != __reject2 && __s[__result] != __reject3)
+ ++__result;
+ return __result;
+}
+
+This should turn into a switch on the character. See PR3253 for some notes on
+codegen.
+
+456.hmmer apparently uses strcspn and strspn a lot. 471.omnetpp uses strspn.
+
+//===---------------------------------------------------------------------===//
+
+"gas" uses this idiom:
+ else if (strchr ("+-/*%|&^:[]()~", *intel_parser.op_string))
+..
+ else if (strchr ("<>", *intel_parser.op_string)
+
+Those should be turned into a switch.
+
+//===---------------------------------------------------------------------===//
+
+252.eon contains this interesting code:
+
+ %3072 = getelementptr [100 x i8]* %tempString, i32 0, i32 0
+ %3073 = call i8* @strcpy(i8* %3072, i8* %3071) nounwind
+ %strlen = call i32 @strlen(i8* %3072) ; uses = 1
+ %endptr = getelementptr [100 x i8]* %tempString, i32 0, i32 %strlen
+ call void @llvm.memcpy.i32(i8* %endptr,
+ i8* getelementptr ([5 x i8]* @"\01LC42", i32 0, i32 0), i32 5, i32 1)
+ %3074 = call i32 @strlen(i8* %endptr) nounwind readonly
+
+This is interesting for a couple reasons. First, in this:
+
+ %3073 = call i8* @strcpy(i8* %3072, i8* %3071) nounwind
+ %strlen = call i32 @strlen(i8* %3072)
+
+The strlen could be replaced with: %strlen = sub %3072, %3073, because the
+strcpy call returns a pointer to the end of the string. Based on that, the
+endptr GEP just becomes equal to 3073, which eliminates a strlen call and GEP.
+
+Second, the memcpy+strlen strlen can be replaced with:
+
+ %3074 = call i32 @strlen([5 x i8]* @"\01LC42") nounwind readonly
+
+Because the destination was just copied into the specified memory buffer. This,
+in turn, can be constant folded to "4".
+
+In other code, it contains:
+
+ %endptr6978 = bitcast i8* %endptr69 to i32*
+ store i32 7107374, i32* %endptr6978, align 1
+ %3167 = call i32 @strlen(i8* %endptr69) nounwind readonly
+
+Which could also be constant folded. Whatever is producing this should probably
+be fixed to leave this as a memcpy from a string.
+
+Further, eon also has an interesting partially redundant strlen call:
+
+bb8: ; preds = %_ZN18eonImageCalculatorC1Ev.exit
+ %682 = getelementptr i8** %argv, i32 6 ; <i8**> [#uses=2]
+ %683 = load i8** %682, align 4 ; <i8*> [#uses=4]
+ %684 = load i8* %683, align 1 ; <i8> [#uses=1]
+ %685 = icmp eq i8 %684, 0 ; <i1> [#uses=1]
+ br i1 %685, label %bb10, label %bb9
+
+bb9: ; preds = %bb8
+ %686 = call i32 @strlen(i8* %683) nounwind readonly
+ %687 = icmp ugt i32 %686, 254 ; <i1> [#uses=1]
+ br i1 %687, label %bb10, label %bb11
+
+bb10: ; preds = %bb9, %bb8
+ %688 = call i32 @strlen(i8* %683) nounwind readonly
+
+This could be eliminated by doing the strlen once in bb8, saving code size and
+improving perf on the bb8->9->10 path.
+
+//===---------------------------------------------------------------------===//
+
+I see an interesting fully redundant call to strlen left in 186.crafty:InputMove
+which looks like:
+ %movetext11 = getelementptr [128 x i8]* %movetext, i32 0, i32 0
+
+
+bb62: ; preds = %bb55, %bb53
+ %promote.0 = phi i32 [ %169, %bb55 ], [ 0, %bb53 ]
+ %171 = call i32 @strlen(i8* %movetext11) nounwind readonly align 1
+ %172 = add i32 %171, -1 ; <i32> [#uses=1]
+ %173 = getelementptr [128 x i8]* %movetext, i32 0, i32 %172
+
+... no stores ...
+ br i1 %or.cond, label %bb65, label %bb72
+
+bb65: ; preds = %bb62
+ store i8 0, i8* %173, align 1
+ br label %bb72
+
+bb72: ; preds = %bb65, %bb62
+ %trank.1 = phi i32 [ %176, %bb65 ], [ -1, %bb62 ]
+ %177 = call i32 @strlen(i8* %movetext11) nounwind readonly align 1
+
+Note that on the bb62->bb72 path, that the %177 strlen call is partially
+redundant with the %171 call. At worst, we could shove the %177 strlen call
+up into the bb65 block moving it out of the bb62->bb72 path. However, note
+that bb65 stores to the string, zeroing out the last byte. This means that on
+that path the value of %177 is actually just %171-1. A sub is cheaper than a
+strlen!
+
+This pattern repeats several times, basically doing:
+
+ A = strlen(P);
+ P[A-1] = 0;
+ B = strlen(P);
+ where it is "obvious" that B = A-1.
+
+//===---------------------------------------------------------------------===//
+
+186.crafty contains this interesting pattern:
+
+%77 = call i8* @strstr(i8* getelementptr ([6 x i8]* @"\01LC5", i32 0, i32 0),
+ i8* %30)
+%phitmp648 = icmp eq i8* %77, getelementptr ([6 x i8]* @"\01LC5", i32 0, i32 0)
+br i1 %phitmp648, label %bb70, label %bb76
+
+bb70: ; preds = %OptionMatch.exit91, %bb69
+ %78 = call i32 @strlen(i8* %30) nounwind readonly align 1 ; <i32> [#uses=1]
+
+This is basically:
+ cststr = "abcdef";
+ if (strstr(cststr, P) == cststr) {
+ x = strlen(P);
+ ...
+
+The strstr call would be significantly cheaper written as:
+
+cststr = "abcdef";
+if (memcmp(P, str, strlen(P)))
+ x = strlen(P);
+
+This is memcmp+strlen instead of strstr. This also makes the strlen fully
+redundant.
+
+//===---------------------------------------------------------------------===//
+
+186.crafty also contains this code:
+
+%1906 = call i32 @strlen(i8* getelementptr ([32 x i8]* @pgn_event, i32 0,i32 0))
+%1907 = getelementptr [32 x i8]* @pgn_event, i32 0, i32 %1906
+%1908 = call i8* @strcpy(i8* %1907, i8* %1905) nounwind align 1
+%1909 = call i32 @strlen(i8* getelementptr ([32 x i8]* @pgn_event, i32 0,i32 0))
+%1910 = getelementptr [32 x i8]* @pgn_event, i32 0, i32 %1909
+
+The last strlen is computable as 1908-@pgn_event, which means 1910=1908.
+
+//===---------------------------------------------------------------------===//
+
+186.crafty has this interesting pattern with the "out.4543" variable:
+
+call void @llvm.memcpy.i32(
+ i8* getelementptr ([10 x i8]* @out.4543, i32 0, i32 0),
+ i8* getelementptr ([7 x i8]* @"\01LC28700", i32 0, i32 0), i32 7, i32 1)
+%101 = call@printf(i8* ... @out.4543, i32 0, i32 0)) nounwind
+
+It is basically doing:
+
+ memcpy(globalarray, "string");
+ printf(..., globalarray);
+
+Anyway, by knowing that printf just reads the memory and forward substituting
+the string directly into the printf, this eliminates reads from globalarray.
+Since this pattern occurs frequently in crafty (due to the "DisplayTime" and
+other similar functions) there are many stores to "out". Once all the printfs
+stop using "out", all that is left is the memcpy's into it. This should allow
+globalopt to remove the "stored only" global.
+
+//===---------------------------------------------------------------------===//
+
+This code:
+
+define inreg i32 @foo(i8* inreg %p) nounwind {
+ %tmp0 = load i8* %p
+ %tmp1 = ashr i8 %tmp0, 5
+ %tmp2 = sext i8 %tmp1 to i32
+ ret i32 %tmp2
+}
+
+could be dagcombine'd to a sign-extending load with a shift.
+For example, on x86 this currently gets this:
+
+ movb (%eax), %al
+ sarb $5, %al
+ movsbl %al, %eax
+
+while it could get this:
+
+ movsbl (%eax), %eax
+ sarl $5, %eax
+
+//===---------------------------------------------------------------------===//
+
+GCC PR31029:
+
+int test(int x) { return 1-x == x; } // --> return false
+int test2(int x) { return 2-x == x; } // --> return x == 1 ?
+
+Always foldable for odd constants, what is the rule for even?
+
+//===---------------------------------------------------------------------===//
+
+PR 3381: GEP to field of size 0 inside a struct could be turned into GEP
+for next field in struct (which is at same address).
+
+For example: store of float into { {{}}, float } could be turned into a store to
+the float directly.
+
+//===---------------------------------------------------------------------===//
+
+#include <math.h>
+double foo(double a) { return sin(a); }
+
+This compiles into this on x86-64 Linux:
+foo:
+ subq $8, %rsp
+ call sin
+ addq $8, %rsp
+ ret
+vs:
+
+foo:
+ jmp sin
+
+//===---------------------------------------------------------------------===//
+
+The arg promotion pass should make use of nocapture to make its alias analysis
+stuff much more precise.
+
+//===---------------------------------------------------------------------===//
+
+The following functions should be optimized to use a select instead of a
+branch (from gcc PR40072):
+
+char char_int(int m) {if(m>7) return 0; return m;}
+int int_char(char m) {if(m>7) return 0; return m;}
+
+//===---------------------------------------------------------------------===//
+
+int func(int a, int b) { if (a & 0x80) b |= 0x80; else b &= ~0x80; return b; }
+
+Generates this:
+
+define i32 @func(i32 %a, i32 %b) nounwind readnone ssp {
+entry:
+ %0 = and i32 %a, 128 ; <i32> [#uses=1]
+ %1 = icmp eq i32 %0, 0 ; <i1> [#uses=1]
+ %2 = or i32 %b, 128 ; <i32> [#uses=1]
+ %3 = and i32 %b, -129 ; <i32> [#uses=1]
+ %b_addr.0 = select i1 %1, i32 %3, i32 %2 ; <i32> [#uses=1]
+ ret i32 %b_addr.0
+}
+
+However, it's functionally equivalent to:
+
+ b = (b & ~0x80) | (a & 0x80);
+
+Which generates this:
+
+define i32 @func(i32 %a, i32 %b) nounwind readnone ssp {
+entry:
+ %0 = and i32 %b, -129 ; <i32> [#uses=1]
+ %1 = and i32 %a, 128 ; <i32> [#uses=1]
+ %2 = or i32 %0, %1 ; <i32> [#uses=1]
+ ret i32 %2
+}
+
+This can be generalized for other forms:
+
+ b = (b & ~0x80) | (a & 0x40) << 1;
+
+//===---------------------------------------------------------------------===//
+
+These two functions produce different code. They shouldn't:
+
+#include <stdint.h>
+
+uint8_t p1(uint8_t b, uint8_t a) {
+ b = (b & ~0xc0) | (a & 0xc0);
+ return (b);
+}
+
+uint8_t p2(uint8_t b, uint8_t a) {
+ b = (b & ~0x40) | (a & 0x40);
+ b = (b & ~0x80) | (a & 0x80);
+ return (b);
+}
+
+define zeroext i8 @p1(i8 zeroext %b, i8 zeroext %a) nounwind readnone ssp {
+entry:
+ %0 = and i8 %b, 63 ; <i8> [#uses=1]
+ %1 = and i8 %a, -64 ; <i8> [#uses=1]
+ %2 = or i8 %1, %0 ; <i8> [#uses=1]
+ ret i8 %2
+}
+
+define zeroext i8 @p2(i8 zeroext %b, i8 zeroext %a) nounwind readnone ssp {
+entry:
+ %0 = and i8 %b, 63 ; <i8> [#uses=1]
+ %.masked = and i8 %a, 64 ; <i8> [#uses=1]
+ %1 = and i8 %a, -128 ; <i8> [#uses=1]
+ %2 = or i8 %1, %0 ; <i8> [#uses=1]
+ %3 = or i8 %2, %.masked ; <i8> [#uses=1]
+ ret i8 %3
+}
+
+//===---------------------------------------------------------------------===//
+
+IPSCCP does not currently propagate argument dependent constants through
+functions where it does not not all of the callers. This includes functions
+with normal external linkage as well as templates, C99 inline functions etc.
+Specifically, it does nothing to:
+
+define i32 @test(i32 %x, i32 %y, i32 %z) nounwind {
+entry:
+ %0 = add nsw i32 %y, %z
+ %1 = mul i32 %0, %x
+ %2 = mul i32 %y, %z
+ %3 = add nsw i32 %1, %2
+ ret i32 %3
+}
+
+define i32 @test2() nounwind {
+entry:
+ %0 = call i32 @test(i32 1, i32 2, i32 4) nounwind
+ ret i32 %0
+}
+
+It would be interesting extend IPSCCP to be able to handle simple cases like
+this, where all of the arguments to a call are constant. Because IPSCCP runs
+before inlining, trivial templates and inline functions are not yet inlined.
+The results for a function + set of constant arguments should be memoized in a
+map.
+
+//===---------------------------------------------------------------------===//
+
+The libcall constant folding stuff should be moved out of SimplifyLibcalls into
+libanalysis' constantfolding logic. This would allow IPSCCP to be able to
+handle simple things like this:
+
+static int foo(const char *X) { return strlen(X); }
+int bar() { return foo("abcd"); }
+
+//===---------------------------------------------------------------------===//
+
+InstCombine should use SimplifyDemandedBits to remove the or instruction:
+
+define i1 @test(i8 %x, i8 %y) {
+ %A = or i8 %x, 1
+ %B = icmp ugt i8 %A, 3
+ ret i1 %B
+}
+
+Currently instcombine calls SimplifyDemandedBits with either all bits or just
+the sign bit, if the comparison is obviously a sign test. In this case, we only
+need all but the bottom two bits from %A, and if we gave that mask to SDB it
+would delete the or instruction for us.
+
+//===---------------------------------------------------------------------===//
+
+functionattrs doesn't know much about memcpy/memset. This function should be
+marked readnone rather than readonly, since it only twiddles local memory, but
+functionattrs doesn't handle memset/memcpy/memmove aggressively:
+
+struct X { int *p; int *q; };
+int foo() {
+ int i = 0, j = 1;
+ struct X x, y;
+ int **p;
+ y.p = &i;
+ x.q = &j;
+ p = __builtin_memcpy (&x, &y, sizeof (int *));
+ return **p;
+}
+
+//===---------------------------------------------------------------------===//
+
+Missed instcombine transformation:
+define i1 @a(i32 %x) nounwind readnone {
+entry:
+ %cmp = icmp eq i32 %x, 30
+ %sub = add i32 %x, -30
+ %cmp2 = icmp ugt i32 %sub, 9
+ %or = or i1 %cmp, %cmp2
+ ret i1 %or
+}
+This should be optimized to a single compare. Testcase derived from gcc.
+
+//===---------------------------------------------------------------------===//
+
+Missed instcombine transformation:
+void b();
+void a(int x) { if (((1<<x)&8)==0) b(); }
+
+The shift should be optimized out. Testcase derived from gcc.
+
+//===---------------------------------------------------------------------===//
+
+Missed instcombine or reassociate transformation:
+int a(int a, int b) { return (a==12)&(b>47)&(b<58); }
+
+The sgt and slt should be combined into a single comparison. Testcase derived
+from gcc.
+
+//===---------------------------------------------------------------------===//
+
+Missed instcombine transformation:
+define i32 @a(i32 %x) nounwind readnone {
+entry:
+ %rem = srem i32 %x, 32
+ %shl = shl i32 1, %rem
+ ret i32 %shl
+}
+
+The srem can be transformed to an and because if x is negative, the shift is
+undefined. Testcase derived from gcc.
+
+//===---------------------------------------------------------------------===//
+
+Missed instcombine/dagcombine transformation:
+define i32 @a(i32 %x, i32 %y) nounwind readnone {
+entry:
+ %mul = mul i32 %y, -8
+ %sub = sub i32 %x, %mul
+ ret i32 %sub
+}
+
+Should compile to something like x+y*8, but currently compiles to an
+inefficient result. Testcase derived from gcc.
+
+//===---------------------------------------------------------------------===//
+
+Missed instcombine/dagcombine transformation:
+define void @lshift_lt(i8 zeroext %a) nounwind {
+entry:
+ %conv = zext i8 %a to i32
+ %shl = shl i32 %conv, 3
+ %cmp = icmp ult i32 %shl, 33
+ br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+ tail call void @bar() nounwind
+ ret void
+
+if.end:
+ ret void
+}
+declare void @bar() nounwind
+
+The shift should be eliminated. Testcase derived from gcc.
+
+//===---------------------------------------------------------------------===//
+
+These compile into different code, one gets recognized as a switch and the
+other doesn't due to phase ordering issues (PR6212):
+
+int test1(int mainType, int subType) {
+ if (mainType == 7)
+ subType = 4;
+ else if (mainType == 9)
+ subType = 6;
+ else if (mainType == 11)
+ subType = 9;
+ return subType;
+}
+
+int test2(int mainType, int subType) {
+ if (mainType == 7)
+ subType = 4;
+ if (mainType == 9)
+ subType = 6;
+ if (mainType == 11)
+ subType = 9;
+ return subType;
+}
+
+//===---------------------------------------------------------------------===//