TODO:
* gpr0 allocation
* implement do-loop -> bdnz transform
+* lmw/stmw pass a la arm load store optimizer for prolog/epilog
===-------------------------------------------------------------------------===
Note that this (and the static variable version) is discussed here for GCC:
http://gcc.gnu.org/ml/gcc-patches/2006-02/msg00133.html
+Here's another example (the sgn function):
+double testf(double a) {
+ return a == 0.0 ? 0.0 : (a > 0.0 ? 1.0 : -1.0);
+}
+
+it produces a BB like this:
+LBB1_1: ; cond_true
+ lis r2, ha16(LCPI1_0)
+ lfs f0, lo16(LCPI1_0)(r2)
+ lis r2, ha16(LCPI1_1)
+ lis r3, ha16(LCPI1_2)
+ lfs f2, lo16(LCPI1_2)(r3)
+ lfs f3, lo16(LCPI1_1)(r2)
+ fsub f0, f0, f1
+ fsel f1, f0, f2, f3
+ blr
+
===-------------------------------------------------------------------------===
PIC Code Gen IPO optimization:
===-------------------------------------------------------------------------===
-Compile this:
-
-int %f1(int %a, int %b) {
- %tmp.1 = and int %a, 15 ; <int> [#uses=1]
- %tmp.3 = and int %b, 240 ; <int> [#uses=1]
- %tmp.4 = or int %tmp.3, %tmp.1 ; <int> [#uses=1]
- ret int %tmp.4
-}
-
-without a copy. We make this currently:
-
-_f1:
- rlwinm r2, r4, 0, 24, 27
- rlwimi r2, r3, 0, 28, 31
- or r3, r2, r2
- blr
-
-The two-addr pass or RA needs to learn when it is profitable to commute an
-instruction to avoid a copy AFTER the 2-addr instruction. The 2-addr pass
-currently only commutes to avoid inserting a copy BEFORE the two addr instr.
-
-===-------------------------------------------------------------------------===
-
Compile offsets from allocas:
int *%test() {
blr
===-------------------------------------------------------------------------===
+
+test/CodeGen/PowerPC/2007-03-24-cntlzd.ll compiles to:
+
+__ZNK4llvm5APInt17countLeadingZerosEv:
+ ld r2, 0(r3)
+ cntlzd r2, r2
+ or r2, r2, r2 <<-- silly.
+ addi r3, r2, -64
+ blr
+
+The dead or is a 'truncate' from 64- to 32-bits.
+
+===-------------------------------------------------------------------------===
+
+We generate horrible ppc code for this:
+
+#define N 2000000
+double a[N],c[N];
+void simpleloop() {
+ int j;
+ for (j=0; j<N; j++)
+ c[j] = a[j];
+}
+
+LBB1_1: ;bb
+ lfdx f0, r3, r4
+ addi r5, r5, 1 ;; Extra IV for the exit value compare.
+ stfdx f0, r2, r4
+ addi r4, r4, 8
+
+ xoris r6, r5, 30 ;; This is due to a large immediate.
+ cmplwi cr0, r6, 33920
+ bne cr0, LBB1_1
+
+//===---------------------------------------------------------------------===//
+
+This:
+ #include <algorithm>
+ inline std::pair<unsigned, bool> full_add(unsigned a, unsigned b)
+ { return std::make_pair(a + b, a + b < a); }
+ bool no_overflow(unsigned a, unsigned b)
+ { return !full_add(a, b).second; }
+
+Should compile to:
+
+__Z11no_overflowjj:
+ add r4,r3,r4
+ subfc r3,r3,r4
+ li r3,0
+ adde r3,r3,r3
+ blr
+
+(or better) not:
+
+__Z11no_overflowjj:
+ add r2, r4, r3
+ cmplw cr7, r2, r3
+ mfcr r2
+ rlwinm r2, r2, 29, 31, 31
+ xori r3, r2, 1
+ blr
+
+//===---------------------------------------------------------------------===//
+
+We compile some FP comparisons into an mfcr with two rlwinms and an or. For
+example:
+#include <math.h>
+int test(double x, double y) { return islessequal(x, y);}
+int test2(double x, double y) { return islessgreater(x, y);}
+int test3(double x, double y) { return !islessequal(x, y);}
+
+Compiles into (all three are similar, but the bits differ):
+
+_test:
+ fcmpu cr7, f1, f2
+ mfcr r2
+ rlwinm r3, r2, 29, 31, 31
+ rlwinm r2, r2, 31, 31, 31
+ or r3, r2, r3
+ blr
+
+GCC compiles this into:
+
+ _test:
+ fcmpu cr7,f1,f2
+ cror 30,28,30
+ mfcr r3
+ rlwinm r3,r3,31,1
+ blr
+
+which is more efficient and can use mfocr. See PR642 for some more context.
+
+//===---------------------------------------------------------------------===//
+
+void foo(float *data, float d) {
+ long i;
+ for (i = 0; i < 8000; i++)
+ data[i] = d;
+}
+void foo2(float *data, float d) {
+ long i;
+ data--;
+ for (i = 0; i < 8000; i++) {
+ data[1] = d;
+ data++;
+ }
+}
+
+These compile to:
+
+_foo:
+ li r2, 0
+LBB1_1: ; bb
+ addi r4, r2, 4
+ stfsx f1, r3, r2
+ cmplwi cr0, r4, 32000
+ mr r2, r4
+ bne cr0, LBB1_1 ; bb
+ blr
+_foo2:
+ li r2, 0
+LBB2_1: ; bb
+ addi r4, r2, 4
+ stfsx f1, r3, r2
+ cmplwi cr0, r4, 32000
+ mr r2, r4
+ bne cr0, LBB2_1 ; bb
+ blr
+
+The 'mr' could be eliminated to folding the add into the cmp better.
+
+//===---------------------------------------------------------------------===//
+Codegen for the following (low-probability) case deteriorated considerably
+when the correctness fixes for unordered comparisons went in (PR 642, 58871).
+It should be possible to recover the code quality described in the comments.
+
+; RUN: llvm-as < %s | llc -march=ppc32 | grep or | count 3
+; This should produce one 'or' or 'cror' instruction per function.
+
+; RUN: llvm-as < %s | llc -march=ppc32 | grep mfcr | count 3
+; PR2964
+
+define i32 @test(double %x, double %y) nounwind {
+entry:
+ %tmp3 = fcmp ole double %x, %y ; <i1> [#uses=1]
+ %tmp345 = zext i1 %tmp3 to i32 ; <i32> [#uses=1]
+ ret i32 %tmp345
+}
+
+define i32 @test2(double %x, double %y) nounwind {
+entry:
+ %tmp3 = fcmp one double %x, %y ; <i1> [#uses=1]
+ %tmp345 = zext i1 %tmp3 to i32 ; <i32> [#uses=1]
+ ret i32 %tmp345
+}
+
+define i32 @test3(double %x, double %y) nounwind {
+entry:
+ %tmp3 = fcmp ugt double %x, %y ; <i1> [#uses=1]
+ %tmp34 = zext i1 %tmp3 to i32 ; <i32> [#uses=1]
+ ret i32 %tmp34
+}
+//===----------------------------------------------------------------------===//
+; RUN: llvm-as < %s | llc -march=ppc32 | not grep fneg
+
+; This could generate FSEL with appropriate flags (FSEL is not IEEE-safe, and
+; should not be generated except with -enable-finite-only-fp-math or the like).
+; With the correctness fixes for PR642 (58871) LowerSELECT_CC would need to
+; recognize a more elaborate tree than a simple SETxx.
+
+define double @test_FNEG_sel(double %A, double %B, double %C) {
+ %D = sub double -0.000000e+00, %A ; <double> [#uses=1]
+ %Cond = fcmp ugt double %D, -0.000000e+00 ; <i1> [#uses=1]
+ %E = select i1 %Cond, double %B, double %C ; <double> [#uses=1]
+ ret double %E
+}
+
projects / oota-llvm.git / blobdiff