+ xorpd LCPI1_0, %xmm0
+ movsd %xmm0, (%esp)
+
+Since we 'know' that this is a 'neg', we can actually "fold" the spill into
+the neg/abs instruction, turning it into an *integer* operation, like this:
+
+ xorl 2147483648, [mem+4] ## 2147483648 = (1 << 31)
+
+you could also use xorb, but xorl is less likely to lead to a partial register
+stall. Here is a contrived testcase:
+
+double a, b, c;
+void test(double *P) {
+ double X = *P;
+ a = X;
+ bar();
+ X = -X;
+ b = X;
+ bar();
+ c = X;
+}
+
+//===---------------------------------------------------------------------===//
+
+handling llvm.memory.barrier on pre SSE2 cpus
+
+should generate:
+lock ; mov %esp, %esp
+
+//===---------------------------------------------------------------------===//
+
+The generated code on x86 for checking for signed overflow on a multiply the
+obvious way is much longer than it needs to be.
+
+int x(int a, int b) {
+ long long prod = (long long)a*b;
+ return prod > 0x7FFFFFFF || prod < (-0x7FFFFFFF-1);
+}
+
+See PR2053 for more details.
+
+//===---------------------------------------------------------------------===//
+
+We should investigate using cdq/ctld (effect: edx = sar eax, 31)
+more aggressively; it should cost the same as a move+shift on any modern
+processor, but it's a lot shorter. Downside is that it puts more
+pressure on register allocation because it has fixed operands.
+
+Example:
+int abs(int x) {return x < 0 ? -x : x;}
+
+gcc compiles this to the following when using march/mtune=pentium2/3/4/m/etc.:
+abs:
+ movl 4(%esp), %eax
+ cltd
+ xorl %edx, %eax
+ subl %edx, %eax
+ ret
+
+//===---------------------------------------------------------------------===//
+
+Consider:
+int test(unsigned long a, unsigned long b) { return -(a < b); }
+
+We currently compile this to:
+
+define i32 @test(i32 %a, i32 %b) nounwind {
+ %tmp3 = icmp ult i32 %a, %b ; <i1> [#uses=1]
+ %tmp34 = zext i1 %tmp3 to i32 ; <i32> [#uses=1]
+ %tmp5 = sub i32 0, %tmp34 ; <i32> [#uses=1]
+ ret i32 %tmp5
+}
+
+and
+
+_test:
+ movl 8(%esp), %eax
+ cmpl %eax, 4(%esp)
+ setb %al
+ movzbl %al, %eax
+ negl %eax
+ ret
+
+Several deficiencies here. First, we should instcombine zext+neg into sext:
+
+define i32 @test2(i32 %a, i32 %b) nounwind {
+ %tmp3 = icmp ult i32 %a, %b ; <i1> [#uses=1]
+ %tmp34 = sext i1 %tmp3 to i32 ; <i32> [#uses=1]
+ ret i32 %tmp34
+}
+
+However, before we can do that, we have to fix the bad codegen that we get for
+sext from bool:
+
+_test2:
+ movl 8(%esp), %eax
+ cmpl %eax, 4(%esp)
+ setb %al
+ movzbl %al, %eax
+ shll $31, %eax
+ sarl $31, %eax
+ ret
+
+This code should be at least as good as the code above. Once this is fixed, we
+can optimize this specific case even more to:
+
+ movl 8(%esp), %eax
+ xorl %ecx, %ecx
+ cmpl %eax, 4(%esp)
+ sbbl %ecx, %ecx
+
+//===---------------------------------------------------------------------===//
+
+Take the following code (from
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16541):
+
+extern unsigned char first_one[65536];
+int FirstOnet(unsigned long long arg1)
+{
+ if (arg1 >> 48)
+ return (first_one[arg1 >> 48]);
+ return 0;
+}
+
+
+The following code is currently generated:
+FirstOnet:
+ movl 8(%esp), %eax
+ cmpl $65536, %eax
+ movl 4(%esp), %ecx
+ jb .LBB1_2 # UnifiedReturnBlock
+.LBB1_1: # ifthen
+ shrl $16, %eax
+ movzbl first_one(%eax), %eax
+ ret
+.LBB1_2: # UnifiedReturnBlock
+ xorl %eax, %eax
+ ret
+
+There are a few possible improvements here:
+1. We should be able to eliminate the dead load into %ecx
+2. We could change the "movl 8(%esp), %eax" into
+ "movzwl 10(%esp), %eax"; this lets us change the cmpl
+ into a testl, which is shorter, and eliminate the shift.
+
+We could also in theory eliminate the branch by using a conditional
+for the address of the load, but that seems unlikely to be worthwhile
+in general.
+
+//===---------------------------------------------------------------------===//
+
+We compile this function:
+
+define i32 @foo(i32 %a, i32 %b, i32 %c, i8 zeroext %d) nounwind {
+entry:
+ %tmp2 = icmp eq i8 %d, 0 ; <i1> [#uses=1]
+ br i1 %tmp2, label %bb7, label %bb
+
+bb: ; preds = %entry
+ %tmp6 = add i32 %b, %a ; <i32> [#uses=1]
+ ret i32 %tmp6
+
+bb7: ; preds = %entry
+ %tmp10 = sub i32 %a, %c ; <i32> [#uses=1]
+ ret i32 %tmp10
+}
+
+to:
+
+_foo:
+ cmpb $0, 16(%esp)
+ movl 12(%esp), %ecx
+ movl 8(%esp), %eax
+ movl 4(%esp), %edx
+ je LBB1_2 # bb7
+LBB1_1: # bb
+ addl %edx, %eax
+ ret
+LBB1_2: # bb7
+ movl %edx, %eax
+ subl %ecx, %eax
+ ret
+
+The coalescer could coalesce "edx" with "eax" to avoid the movl in LBB1_2
+if it commuted the addl in LBB1_1.
+
+//===---------------------------------------------------------------------===//
+
+See rdar://4653682.
+
+From flops:
+
+LBB1_15: # bb310
+ cvtss2sd LCPI1_0, %xmm1
+ addsd %xmm1, %xmm0
+ movsd 176(%esp), %xmm2
+ mulsd %xmm0, %xmm2
+ movapd %xmm2, %xmm3
+ mulsd %xmm3, %xmm3
+ movapd %xmm3, %xmm4
+ mulsd LCPI1_23, %xmm4
+ addsd LCPI1_24, %xmm4
+ mulsd %xmm3, %xmm4
+ addsd LCPI1_25, %xmm4
+ mulsd %xmm3, %xmm4
+ addsd LCPI1_26, %xmm4
+ mulsd %xmm3, %xmm4
+ addsd LCPI1_27, %xmm4
+ mulsd %xmm3, %xmm4
+ addsd LCPI1_28, %xmm4
+ mulsd %xmm3, %xmm4
+ addsd %xmm1, %xmm4
+ mulsd %xmm2, %xmm4
+ movsd 152(%esp), %xmm1
+ addsd %xmm4, %xmm1
+ movsd %xmm1, 152(%esp)
+ incl %eax
+ cmpl %eax, %esi
+ jge LBB1_15 # bb310
+LBB1_16: # bb358.loopexit
+ movsd 152(%esp), %xmm0
+ addsd %xmm0, %xmm0
+ addsd LCPI1_22, %xmm0
+ movsd %xmm0, 152(%esp)
+
+Rather than spilling the result of the last addsd in the loop, we should have
+insert a copy to split the interval (one for the duration of the loop, one
+extending to the fall through). The register pressure in the loop isn't high
+enough to warrant the spill.
+
+Also check why xmm7 is not used at all in the function.
+
+//===---------------------------------------------------------------------===//
+
+Legalize loses track of the fact that bools are always zero extended when in
+memory. This causes us to compile abort_gzip (from 164.gzip) from:
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target triple = "i386-apple-darwin8"
+@in_exit.4870.b = internal global i1 false ; <i1*> [#uses=2]
+define fastcc void @abort_gzip() noreturn nounwind {
+entry:
+ %tmp.b.i = load i1* @in_exit.4870.b ; <i1> [#uses=1]
+ br i1 %tmp.b.i, label %bb.i, label %bb4.i
+bb.i: ; preds = %entry
+ tail call void @exit( i32 1 ) noreturn nounwind
+ unreachable
+bb4.i: ; preds = %entry
+ store i1 true, i1* @in_exit.4870.b
+ tail call void @exit( i32 1 ) noreturn nounwind
+ unreachable
+}
+declare void @exit(i32) noreturn nounwind
+
+into:
+
+_abort_gzip:
+ subl $12, %esp
+ movb _in_exit.4870.b, %al
+ notb %al
+ testb $1, %al
+ jne LBB1_2 ## bb4.i
+LBB1_1: ## bb.i
+ ...
+
+//===---------------------------------------------------------------------===//
+
+We compile:
+
+int test(int x, int y) {
+ return x-y-1;
+}
+
+into (-m64):
+
+_test:
+ decl %edi
+ movl %edi, %eax
+ subl %esi, %eax
+ ret
+
+it would be better to codegen as: x+~y (notl+addl)
+
+//===---------------------------------------------------------------------===//
+
+This code:
+
+int foo(const char *str,...)
+{
+ __builtin_va_list a; int x;
+ __builtin_va_start(a,str); x = __builtin_va_arg(a,int); __builtin_va_end(a);
+ return x;
+}
+
+gets compiled into this on x86-64:
+ subq $200, %rsp
+ movaps %xmm7, 160(%rsp)
+ movaps %xmm6, 144(%rsp)
+ movaps %xmm5, 128(%rsp)
+ movaps %xmm4, 112(%rsp)
+ movaps %xmm3, 96(%rsp)
+ movaps %xmm2, 80(%rsp)
+ movaps %xmm1, 64(%rsp)
+ movaps %xmm0, 48(%rsp)
+ movq %r9, 40(%rsp)
+ movq %r8, 32(%rsp)
+ movq %rcx, 24(%rsp)
+ movq %rdx, 16(%rsp)
+ movq %rsi, 8(%rsp)
+ leaq (%rsp), %rax
+ movq %rax, 192(%rsp)
+ leaq 208(%rsp), %rax
+ movq %rax, 184(%rsp)
+ movl $48, 180(%rsp)
+ movl $8, 176(%rsp)
+ movl 176(%rsp), %eax
+ cmpl $47, %eax
+ jbe .LBB1_3 # bb
+.LBB1_1: # bb3
+ movq 184(%rsp), %rcx
+ leaq 8(%rcx), %rax
+ movq %rax, 184(%rsp)
+.LBB1_2: # bb4
+ movl (%rcx), %eax
+ addq $200, %rsp
+ ret
+.LBB1_3: # bb
+ movl %eax, %ecx
+ addl $8, %eax
+ addq 192(%rsp), %rcx
+ movl %eax, 176(%rsp)
+ jmp .LBB1_2 # bb4
+
+gcc 4.3 generates:
+ subq $96, %rsp
+.LCFI0:
+ leaq 104(%rsp), %rax
+ movq %rsi, -80(%rsp)
+ movl $8, -120(%rsp)
+ movq %rax, -112(%rsp)
+ leaq -88(%rsp), %rax
+ movq %rax, -104(%rsp)
+ movl $8, %eax
+ cmpl $48, %eax
+ jb .L6
+ movq -112(%rsp), %rdx
+ movl (%rdx), %eax
+ addq $96, %rsp
+ ret
+ .p2align 4,,10
+ .p2align 3
+.L6:
+ mov %eax, %edx
+ addq -104(%rsp), %rdx
+ addl $8, %eax
+ movl %eax, -120(%rsp)
+ movl (%rdx), %eax
+ addq $96, %rsp
+ ret
+
+and it gets compiled into this on x86:
+ pushl %ebp
+ movl %esp, %ebp
+ subl $4, %esp
+ leal 12(%ebp), %eax
+ movl %eax, -4(%ebp)
+ leal 16(%ebp), %eax
+ movl %eax, -4(%ebp)
+ movl 12(%ebp), %eax
+ addl $4, %esp
+ popl %ebp
+ ret
+
+gcc 4.3 generates:
+ pushl %ebp
+ movl %esp, %ebp
+ movl 12(%ebp), %eax
+ popl %ebp
+ ret
+
+//===---------------------------------------------------------------------===//
+
+Teach tblgen not to check bitconvert source type in some cases. This allows us
+to consolidate the following patterns in X86InstrMMX.td:
+
+def : Pat<(v2i32 (bitconvert (i64 (vector_extract (v2i64 VR128:$src),
+ (iPTR 0))))),
+ (v2i32 (MMX_MOVDQ2Qrr VR128:$src))>;
+def : Pat<(v4i16 (bitconvert (i64 (vector_extract (v2i64 VR128:$src),
+ (iPTR 0))))),
+ (v4i16 (MMX_MOVDQ2Qrr VR128:$src))>;
+def : Pat<(v8i8 (bitconvert (i64 (vector_extract (v2i64 VR128:$src),
+ (iPTR 0))))),
+ (v8i8 (MMX_MOVDQ2Qrr VR128:$src))>;
+
+There are other cases in various td files.
+
+//===---------------------------------------------------------------------===//
+
+Take something like the following on x86-32:
+unsigned a(unsigned long long x, unsigned y) {return x % y;}
+
+We currently generate a libcall, but we really shouldn't: the expansion is
+shorter and likely faster than the libcall. The expected code is something
+like the following:
+
+ movl 12(%ebp), %eax
+ movl 16(%ebp), %ecx
+ xorl %edx, %edx
+ divl %ecx
+ movl 8(%ebp), %eax
+ divl %ecx
+ movl %edx, %eax
+ ret
+
+A similar code sequence works for division.
+
+//===---------------------------------------------------------------------===//
+
+These should compile to the same code, but the later codegen's to useless
+instructions on X86. This may be a trivial dag combine (GCC PR7061):
+
+struct s1 { unsigned char a, b; };
+unsigned long f1(struct s1 x) {
+ return x.a + x.b;
+}
+struct s2 { unsigned a: 8, b: 8; };
+unsigned long f2(struct s2 x) {
+ return x.a + x.b;
+}
+
+//===---------------------------------------------------------------------===//
+
+We currently compile this:
+
+define i32 @func1(i32 %v1, i32 %v2) nounwind {
+entry:
+ %t = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %v1, i32 %v2)
+ %sum = extractvalue {i32, i1} %t, 0
+ %obit = extractvalue {i32, i1} %t, 1
+ br i1 %obit, label %overflow, label %normal
+normal:
+ ret i32 %sum
+overflow:
+ call void @llvm.trap()
+ unreachable
+}
+declare {i32, i1} @llvm.sadd.with.overflow.i32(i32, i32)
+declare void @llvm.trap()
+
+to:
+
+_func1:
+ movl 4(%esp), %eax
+ addl 8(%esp), %eax
+ jo LBB1_2 ## overflow
+LBB1_1: ## normal
+ ret
+LBB1_2: ## overflow
+ ud2
+
+it would be nice to produce "into" someday.
+
+//===---------------------------------------------------------------------===//
+
+This code:
+
+void vec_mpys1(int y[], const int x[], int scaler) {
+int i;
+for (i = 0; i < 150; i++)
+ y[i] += (((long long)scaler * (long long)x[i]) >> 31);
+}
+
+Compiles to this loop with GCC 3.x:
+
+.L5:
+ movl %ebx, %eax
+ imull (%edi,%ecx,4)
+ shrdl $31, %edx, %eax
+ addl %eax, (%esi,%ecx,4)
+ incl %ecx
+ cmpl $149, %ecx
+ jle .L5
+
+llvm-gcc compiles it to the much uglier:
+
+LBB1_1: ## bb1
+ movl 24(%esp), %eax
+ movl (%eax,%edi,4), %ebx
+ movl %ebx, %ebp
+ imull %esi, %ebp
+ movl %ebx, %eax
+ mull %ecx
+ addl %ebp, %edx
+ sarl $31, %ebx
+ imull %ecx, %ebx
+ addl %edx, %ebx
+ shldl $1, %eax, %ebx
+ movl 20(%esp), %eax
+ addl %ebx, (%eax,%edi,4)
+ incl %edi
+ cmpl $150, %edi
+ jne LBB1_1 ## bb1
+
+//===---------------------------------------------------------------------===//
+
+Test instructions can be eliminated by using EFLAGS values from arithmetic
+instructions. This is currently not done for mul, and, or, xor, neg, shl,
+sra, srl, shld, shrd, atomic ops, and others. It is also currently not done
+for read-modify-write instructions. It is also current not done if the
+OF or CF flags are needed.
+
+The shift operators have the complication that when the shift count is
+zero, EFLAGS is not set, so they can only subsume a test instruction if
+the shift count is known to be non-zero. Also, using the EFLAGS value
+from a shift is apparently very slow on some x86 implementations.
+
+In read-modify-write instructions, the root node in the isel match is
+the store, and isel has no way for the use of the EFLAGS result of the
+arithmetic to be remapped to the new node.
+
+Add and subtract instructions set OF on signed overflow and CF on unsiged
+overflow, while test instructions always clear OF and CF. In order to
+replace a test with an add or subtract in a situation where OF or CF is
+needed, codegen must be able to prove that the operation cannot see
+signed or unsigned overflow, respectively.
+
+//===---------------------------------------------------------------------===//
+
+memcpy/memmove do not lower to SSE copies when possible. A silly example is:
+define <16 x float> @foo(<16 x float> %A) nounwind {
+ %tmp = alloca <16 x float>, align 16
+ %tmp2 = alloca <16 x float>, align 16
+ store <16 x float> %A, <16 x float>* %tmp
+ %s = bitcast <16 x float>* %tmp to i8*
+ %s2 = bitcast <16 x float>* %tmp2 to i8*
+ call void @llvm.memcpy.i64(i8* %s, i8* %s2, i64 64, i32 16)
+ %R = load <16 x float>* %tmp2
+ ret <16 x float> %R
+}
+
+declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
+
+which compiles to:
+
+_foo:
+ subl $140, %esp
+ movaps %xmm3, 112(%esp)
+ movaps %xmm2, 96(%esp)
+ movaps %xmm1, 80(%esp)
+ movaps %xmm0, 64(%esp)
+ movl 60(%esp), %eax
+ movl %eax, 124(%esp)
+ movl 56(%esp), %eax
+ movl %eax, 120(%esp)
+ movl 52(%esp), %eax
+ <many many more 32-bit copies>
+ movaps (%esp), %xmm0
+ movaps 16(%esp), %xmm1
+ movaps 32(%esp), %xmm2
+ movaps 48(%esp), %xmm3
+ addl $140, %esp
+ ret
+
+On Nehalem, it may even be cheaper to just use movups when unaligned than to
+fall back to lower-granularity chunks.
+
+//===---------------------------------------------------------------------===//
+
+Implement processor-specific optimizations for parity with GCC on these
+processors. GCC does two optimizations:
+
+1. ix86_pad_returns inserts a noop before ret instructions if immediately
+ preceeded by a conditional branch or is the target of a jump.
+2. ix86_avoid_jump_misspredicts inserts noops in cases where a 16-byte block of
+ code contains more than 3 branches.
+
+The first one is done for all AMDs, Core2, and "Generic"
+The second one is done for: Atom, Pentium Pro, all AMDs, Pentium 4, Nocona,
+ Core 2, and "Generic"
+
+//===---------------------------------------------------------------------===//
+
+Testcase:
+int a(int x) { return (x & 127) > 31; }
+
+Current output:
+ movl 4(%esp), %eax
+ andl $127, %eax
+ cmpl $31, %eax
+ seta %al
+ movzbl %al, %eax
+ ret
+
+Ideal output:
+ xorl %eax, %eax
+ testl $96, 4(%esp)
+ setne %al
+ ret
+
+This should definitely be done in instcombine, canonicalizing the range
+condition into a != condition. We get this IR:
+
+define i32 @a(i32 %x) nounwind readnone {
+entry:
+ %0 = and i32 %x, 127 ; <i32> [#uses=1]
+ %1 = icmp ugt i32 %0, 31 ; <i1> [#uses=1]
+ %2 = zext i1 %1 to i32 ; <i32> [#uses=1]
+ ret i32 %2
+}
+
+Instcombine prefers to strength reduce relational comparisons to equality
+comparisons when possible, this should be another case of that. This could
+be handled pretty easily in InstCombiner::visitICmpInstWithInstAndIntCst, but it
+looks like InstCombiner::visitICmpInstWithInstAndIntCst should really already
+be redesigned to use ComputeMaskedBits and friends.
+
+
+//===---------------------------------------------------------------------===//
+Testcase:
+int x(int a) { return (a&0xf0)>>4; }
+
+Current output:
+ movl 4(%esp), %eax
+ shrl $4, %eax
+ andl $15, %eax