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[CodeGenPrepare] Improved logic to speculate calls to cttz/ctlz.
This patch improves the logic added at revision 224899 (see review D6728) that teaches the backend when it is profitable to speculate calls to cttz/ctlz. The original algorithm conservatively avoided speculating more than one instruction from a basic block in a control flow grap modelling an if-statement. In particular, the only allowed instruction (excluding the terminator) was a call to cttz/ctlz. However, there are cases where we could be less conservative and still be able to speculate a call to cttz/ctlz. With this patch, CodeGenPrepare now tries to speculate a cttz/ctlz if the result is zero extended/truncated in the same basic block, and the zext/trunc instruction is "free" for the target. Added new test cases to CodeGen/X86/cttz-ctlz.ll Differential Revision: http://reviews.llvm.org/D6853 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225274 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrea Di Biagio
parent
46cb54c0fb
commit
e46783d5b7
@ -4008,15 +4008,41 @@ static bool OptimizeBranchInst(BranchInst *BrInst, const TargetLowering &TLI) {
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// See if ThenBB contains only one instruction (excluding the
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// terminator and DbgInfoIntrinsic calls).
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IntrinsicInst *II = nullptr;
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CastInst *CI = nullptr;
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for (BasicBlock::iterator I = ThenBB->begin(),
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E = std::prev(ThenBB->end()); I != E; ++I) {
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// Skip debug info.
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if (isa<DbgInfoIntrinsic>(I))
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continue;
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if (II)
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// Avoid speculating more than one instruction.
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return false;
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// Check if this is a zero extension or a truncate of a previously
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// matched call to intrinsic cttz/ctlz.
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if (II) {
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// Early exit if we already found a "free" zero extend/truncate.
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if (CI)
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return false;
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Type *SrcTy = II->getType();
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Type *DestTy = I->getType();
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Value *V;
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if (match(cast<Instruction>(I), m_ZExt(m_Value(V))) && V == II) {
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// Speculate this zero extend only if it is "free" for the target.
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if (TLI.isZExtFree(SrcTy, DestTy)) {
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CI = cast<CastInst>(I);
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continue;
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}
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} else if (match(cast<Instruction>(I), m_Trunc(m_Value(V))) && V == II) {
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// Speculate this truncate only if it is "free" for the target.
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if (TLI.isTruncateFree(SrcTy, DestTy)) {
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CI = cast<CastInst>(I);
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continue;
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}
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} else {
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// Avoid speculating more than one instruction.
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return false;
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}
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}
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// See if this is a call to intrinsic cttz/ctlz.
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if (match(cast<Instruction>(I), m_Intrinsic<Intrinsic::cttz>())) {
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@ -4041,11 +4067,14 @@ static bool OptimizeBranchInst(BranchInst *BrInst, const TargetLowering &TLI) {
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Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
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Value *OrigV = PN->getIncomingValueForBlock(EntryBB);
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if (!OrigV || ThenV != II)
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if (!OrigV)
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return false;
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if (ThenV != II && (!CI || ThenV != CI))
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return false;
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if (ConstantInt *CInt = dyn_cast<ConstantInt>(OrigV)) {
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unsigned BitWidth = ThenV->getType()->getIntegerBitWidth();
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unsigned BitWidth = II->getType()->getIntegerBitWidth();
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// Don't try to simplify this phi node if 'ThenV' is a cttz/ctlz
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// intrinsic call, but 'OrigV' is not equal to the 'size-of' in bits
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@ -4070,7 +4099,7 @@ static bool OptimizeBranchInst(BranchInst *BrInst, const TargetLowering &TLI) {
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ConstantInt::getFalse(II->getContext()) };
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Module *M = EntryBB->getParent()->getParent();
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Value *IF = Intrinsic::getDeclaration(M, II->getIntrinsicID(), Ty);
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IRBuilder<> Builder(BrInst);
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IRBuilder<> Builder(II);
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Instruction *NewI = Builder.CreateCall(IF, Args);
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// Replace the old call to cttz/ctlz.
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@ -241,6 +241,178 @@ cond.end: ; preds = %entry, %cond.true
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ret i16 %cond
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}
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; The following tests verify that calls to cttz/ctlz are speculated even if
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; basic block %cond.true has an extra zero extend/truncate which is "free"
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; for the target.
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define i64 @test1e(i32 %x) {
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; ALL-LABEL: @test1e(
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; LZCNT: icmp eq i32 %x, 0
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; LZCNT: call i32 @llvm.cttz.i32(i32 %x, i1 true)
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; BMI: call i32 @llvm.cttz.i32(i32 %x, i1 false)
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; GENERIC: icmp eq i32 %x, 0
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; GENERIC: call i32 @llvm.cttz.i32(i32 %x, i1 true)
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entry:
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%tobool = icmp eq i32 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
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%phitmp2 = zext i32 %0 to i64
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i64 [ %phitmp2, %cond.true ], [ 32, %entry ]
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ret i64 %cond
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}
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define i32 @test2e(i64 %x) {
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; ALL-LABEL: @test2e(
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; LZCNT: icmp eq i64 %x, 0
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; LZCNT: call i64 @llvm.cttz.i64(i64 %x, i1 true)
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; BMI: call i64 @llvm.cttz.i64(i64 %x, i1 false)
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; GENERIC: icmp eq i64 %x, 0
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; GENERIC: call i64 @llvm.cttz.i64(i64 %x, i1 true)
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entry:
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%tobool = icmp eq i64 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
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%cast = trunc i64 %0 to i32
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i32 [ %cast, %cond.true ], [ 64, %entry ]
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ret i32 %cond
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}
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define i64 @test3e(i32 %x) {
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; ALL-LABEL: @test3e(
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; BMI: icmp eq i32 %x, 0
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; BMI: call i32 @llvm.ctlz.i32(i32 %x, i1 true)
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; LZCNT: call i32 @llvm.ctlz.i32(i32 %x, i1 false)
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; GENERIC: icmp eq i32 %x, 0
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; GENERIC: call i32 @llvm.ctlz.i32(i32 %x, i1 true)
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entry:
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%tobool = icmp eq i32 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
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%phitmp2 = zext i32 %0 to i64
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i64 [ %phitmp2, %cond.true ], [ 32, %entry ]
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ret i64 %cond
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}
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define i32 @test4e(i64 %x) {
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; ALL-LABEL: @test4e(
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; BMI: icmp eq i64 %x, 0
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; BMI: call i64 @llvm.ctlz.i64(i64 %x, i1 true)
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; LZCNT: call i64 @llvm.ctlz.i64(i64 %x, i1 false)
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; GENERIC: icmp eq i64 %x, 0
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; GENERIC: call i64 @llvm.ctlz.i64(i64 %x, i1 true)
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entry:
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%tobool = icmp eq i64 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
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%cast = trunc i64 %0 to i32
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i32 [ %cast, %cond.true ], [ 64, %entry ]
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ret i32 %cond
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}
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define i16 @test5e(i64 %x) {
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; ALL-LABEL: @test5e(
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; BMI: icmp eq i64 %x, 0
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; BMI: call i64 @llvm.ctlz.i64(i64 %x, i1 true)
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; LZCNT: call i64 @llvm.ctlz.i64(i64 %x, i1 false)
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; GENERIC: icmp eq i64 %x, 0
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; GENERIC: call i64 @llvm.ctlz.i64(i64 %x, i1 true)
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entry:
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%tobool = icmp eq i64 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
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%cast = trunc i64 %0 to i16
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i16 [ %cast, %cond.true ], [ 64, %entry ]
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ret i16 %cond
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}
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define i16 @test6e(i32 %x) {
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; ALL-LABEL: @test6e(
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; BMI: icmp eq i32 %x, 0
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; BMI: call i32 @llvm.ctlz.i32(i32 %x, i1 true)
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; LZCNT: call i32 @llvm.ctlz.i32(i32 %x, i1 false)
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; GENERIC: icmp eq i32 %x, 0
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; GENERIC: call i32 @llvm.ctlz.i32(i32 %x, i1 true)
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entry:
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%tobool = icmp eq i32 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
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%cast = trunc i32 %0 to i16
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i16 [ %cast, %cond.true ], [ 32, %entry ]
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ret i16 %cond
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}
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define i16 @test7e(i64 %x) {
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; ALL-LABEL: @test7e(
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; LZCNT: icmp eq i64 %x, 0
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; LZCNT: call i64 @llvm.cttz.i64(i64 %x, i1 true)
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; BMI: call i64 @llvm.cttz.i64(i64 %x, i1 false)
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; GENERIC: icmp eq i64 %x, 0
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; GENERIC: call i64 @llvm.cttz.i64(i64 %x, i1 true)
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entry:
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%tobool = icmp eq i64 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
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%cast = trunc i64 %0 to i16
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i16 [ %cast, %cond.true ], [ 64, %entry ]
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ret i16 %cond
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}
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define i16 @test8e(i32 %x) {
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; ALL-LABEL: @test8e(
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; LZCNT: icmp eq i32 %x, 0
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; LZCNT: call i32 @llvm.cttz.i32(i32 %x, i1 true)
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; BMI: call i32 @llvm.cttz.i32(i32 %x, i1 false)
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; GENERIC: icmp eq i32 %x, 0
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; GENERIC: call i32 @llvm.cttz.i32(i32 %x, i1 true)
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entry:
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%tobool = icmp eq i32 %x, 0
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br i1 %tobool, label %cond.end, label %cond.true
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cond.true: ; preds = %entry
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%0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
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%cast = trunc i32 %0 to i16
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br label %cond.end
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cond.end: ; preds = %entry, %cond.true
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%cond = phi i16 [ %cast, %cond.true ], [ 32, %entry ]
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ret i16 %cond
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}
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declare i64 @llvm.ctlz.i64(i64, i1)
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declare i32 @llvm.ctlz.i32(i32, i1)
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