[llvm-commits] [llvm] r97766 - in /llvm/trunk: lib/Target/X86/X86InstrInfo.cpp test/CodeGen/X86/jump-opt.ll test/FrontendC/2008-07-29-EHLabel.ll
Bill Wendling
isanbard at gmail.com
Thu Mar 4 16:24:26 PST 2010
Author: void
Date: Thu Mar 4 18:24:26 2010
New Revision: 97766
URL: http://llvm.org/viewvc/llvm-project?rev=97766&view=rev
Log:
Micro-optimization:
This code:
float floatingPointComparison(float x, float y) {
double product = (double)x * y;
if (product == 0.0)
return product;
return product - 1.0;
}
produces this:
_floatingPointComparison:
0000000000000000 cvtss2sd %xmm1,%xmm1
0000000000000004 cvtss2sd %xmm0,%xmm0
0000000000000008 mulsd %xmm1,%xmm0
000000000000000c pxor %xmm1,%xmm1
0000000000000010 ucomisd %xmm1,%xmm0
0000000000000014 jne 0x00000004
0000000000000016 jp 0x00000002
0000000000000018 jmp 0x00000008
000000000000001a addsd 0x00000006(%rip),%xmm0
0000000000000022 cvtsd2ss %xmm0,%xmm0
0000000000000026 ret
The "jne/jp/jmp" sequence can be reduced to this instead:
_floatingPointComparison:
0000000000000000 cvtss2sd %xmm1,%xmm1
0000000000000004 cvtss2sd %xmm0,%xmm0
0000000000000008 mulsd %xmm1,%xmm0
000000000000000c pxor %xmm1,%xmm1
0000000000000010 ucomisd %xmm1,%xmm0
0000000000000014 jp 0x00000002
0000000000000016 je 0x00000008
0000000000000018 addsd 0x00000006(%rip),%xmm0
0000000000000020 cvtsd2ss %xmm0,%xmm0
0000000000000024 ret
for a savings of 2 bytes.
This xform can happen when we recognize that jne and jp jump to the same "true"
MBB, the unconditional jump would jump to the "false" MBB, and the "true" branch
is the fall-through MBB.
Added:
llvm/trunk/test/CodeGen/X86/jump-opt.ll
Modified:
llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
llvm/trunk/test/FrontendC/2008-07-29-EHLabel.ll (props changed)
Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.cpp?rev=97766&r1=97765&r2=97766&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86InstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86InstrInfo.cpp Thu Mar 4 18:24:26 2010
@@ -1786,6 +1786,7 @@
const SmallVectorImpl<MachineOperand> &Cond) const {
// FIXME this should probably have a DebugLoc operand
DebugLoc dl = DebugLoc::getUnknownLoc();
+
// Shouldn't be a fall through.
assert(TBB && "InsertBranch must not be told to insert a fallthrough");
assert((Cond.size() == 1 || Cond.size() == 0) &&
@@ -1799,34 +1800,72 @@
}
// Conditional branch.
+ const MachineBasicBlock *NextBB = next(&MBB);
unsigned Count = 0;
X86::CondCode CC = (X86::CondCode)Cond[0].getImm();
+
+ // In a two-way conditional branch, if the fall-through block is the
+ // "false" branch of the conditional jumps, we can cut out the
+ // unconditional jump by rearranging the conditional jumps. This saves a
+ // few bytes and improves performance. I.e., for COND_NE_OR_P:
+ //
+ // JNE L1
+ // JP L1
+ // JMP L2
+ // L1:
+ // ...
+ // L2:
+ // ...
+ //
+ // to:
+ //
+ // JP L1
+ // JE L2
+ // L1:
+ // ...
+ // L2:
+ // ...
+ //
+ // Similarly for COND_NP_OR_E.
switch (CC) {
+ default:
+ BuildMI(&MBB, dl, get(GetCondBranchFromCond(CC))).addMBB(TBB);
+ ++Count;
+ break;
case X86::COND_NP_OR_E:
// Synthesize NP_OR_E with two branches.
- BuildMI(&MBB, dl, get(X86::JNP_4)).addMBB(TBB);
- ++Count;
- BuildMI(&MBB, dl, get(X86::JE_4)).addMBB(TBB);
- ++Count;
+ if (FBB && FBB == NextBB) {
+ BuildMI(&MBB, dl, get(X86::JNP_4)).addMBB(TBB);
+ BuildMI(&MBB, dl, get(X86::JNE_4)).addMBB(FBB);
+ FBB = 0;
+ } else {
+ BuildMI(&MBB, dl, get(X86::JNP_4)).addMBB(TBB);
+ BuildMI(&MBB, dl, get(X86::JE_4)).addMBB(TBB);
+ }
+
+ Count += 2;
break;
case X86::COND_NE_OR_P:
// Synthesize NE_OR_P with two branches.
- BuildMI(&MBB, dl, get(X86::JNE_4)).addMBB(TBB);
- ++Count;
- BuildMI(&MBB, dl, get(X86::JP_4)).addMBB(TBB);
- ++Count;
+ if (FBB && FBB == NextBB) {
+ BuildMI(&MBB, dl, get(X86::JP_4)).addMBB(TBB);
+ BuildMI(&MBB, dl, get(X86::JE_4)).addMBB(FBB);
+ FBB = 0;
+ } else {
+ BuildMI(&MBB, dl, get(X86::JNE_4)).addMBB(TBB);
+ BuildMI(&MBB, dl, get(X86::JP_4)).addMBB(TBB);
+ }
+
+ Count += 2;
break;
- default: {
- unsigned Opc = GetCondBranchFromCond(CC);
- BuildMI(&MBB, dl, get(Opc)).addMBB(TBB);
- ++Count;
- }
}
+
if (FBB) {
// Two-way Conditional branch. Insert the second branch.
BuildMI(&MBB, dl, get(X86::JMP_4)).addMBB(FBB);
++Count;
}
+
return Count;
}
Added: llvm/trunk/test/CodeGen/X86/jump-opt.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/jump-opt.ll?rev=97766&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/jump-opt.ll (added)
+++ llvm/trunk/test/CodeGen/X86/jump-opt.ll Thu Mar 4 18:24:26 2010
@@ -0,0 +1,22 @@
+; RUN: llc < %s -mtriple=i386-apple-darwin10 | FileCheck %s
+
+; <rdar://problem/7598384>
+define float @test1(float %x, float %y) nounwind readnone optsize ssp {
+; CHECK: jp
+; CHECK-NEXT: je
+entry:
+ %0 = fpext float %x to double
+ %1 = fpext float %y to double
+ %2 = fmul double %0, %1
+ %3 = fcmp oeq double %2, 0.000000e+00
+ br i1 %3, label %bb2, label %bb1
+
+bb1:
+ %4 = fadd double %2, -1.000000e+00
+ br label %bb2
+
+bb2:
+ %.0.in = phi double [ %4, %bb1 ], [ %2, %entry ]
+ %.0 = fptrunc double %.0.in to float
+ ret float %.0
+}
Propchange: llvm/trunk/test/FrontendC/2008-07-29-EHLabel.ll
------------------------------------------------------------------------------
(empty)
More information about the llvm-commits
mailing list