[llvm] r237452 - Allow min/max detection to see through casts.
James Molloy
james.molloy at arm.com
Fri May 15 09:04:50 PDT 2015
Author: jamesm
Date: Fri May 15 11:04:50 2015
New Revision: 237452
URL: http://llvm.org/viewvc/llvm-project?rev=237452&view=rev
Log:
Allow min/max detection to see through casts.
This teaches the min/max idiom detector in ValueTracking to see through
casts such as SExt/ZExt/Trunc. SCEV can already do this, so we're bringing
non-SCEV analyses up to the same level.
The returned LHS/RHS will not match the type of the original SelectInst
any more, so a CastOp is returned too to inform the caller how to
convert to the SelectInst's type.
No in-tree users yet; this will be used by InstCombine in a followup.
Modified:
llvm/trunk/include/llvm/Analysis/ValueTracking.h
llvm/trunk/lib/Analysis/ValueTracking.cpp
Modified: llvm/trunk/include/llvm/Analysis/ValueTracking.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ValueTracking.h?rev=237452&r1=237451&r2=237452&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ValueTracking.h (original)
+++ llvm/trunk/include/llvm/Analysis/ValueTracking.h Fri May 15 11:04:50 2015
@@ -16,6 +16,7 @@
#define LLVM_ANALYSIS_VALUETRACKING_H
#include "llvm/ADT/ArrayRef.h"
+#include "llvm/IR/Instruction.h"
#include "llvm/Support/DataTypes.h"
namespace llvm {
@@ -280,7 +281,21 @@ namespace llvm {
};
/// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
/// and providing the out parameter results if we successfully match.
- SelectPatternFlavor matchSelectPattern(Value *V, Value *&LHS, Value *&RHS);
+ ///
+ /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
+ /// not match that of the original select. If this is the case, the cast
+ /// operation (one of Trunc,SExt,Zext) that must be done to transform the
+ /// type of LHS and RHS into the type of V is returned in CastOp.
+ ///
+ /// For example:
+ /// %1 = icmp slt i32 %a, i32 4
+ /// %2 = sext i32 %a to i64
+ /// %3 = select i1 %1, i64 %2, i64 4
+ ///
+ /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
+ ///
+ SelectPatternFlavor matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
+ Instruction::CastOps *CastOp = nullptr);
} // end namespace llvm
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=237452&r1=237451&r2=237452&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Fri May 15 11:04:50 2015
@@ -3220,20 +3220,10 @@ OverflowResult llvm::computeOverflowForU
return OverflowResult::MayOverflow;
}
-SelectPatternFlavor llvm::matchSelectPattern(Value *V,
- Value *&LHS, Value *&RHS) {
- SelectInst *SI = dyn_cast<SelectInst>(V);
- if (!SI) return SPF_UNKNOWN;
-
- ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
- if (!ICI) return SPF_UNKNOWN;
-
- ICmpInst::Predicate Pred = ICI->getPredicate();
- Value *CmpLHS = ICI->getOperand(0);
- Value *CmpRHS = ICI->getOperand(1);
- Value *TrueVal = SI->getTrueValue();
- Value *FalseVal = SI->getFalseValue();
-
+static SelectPatternFlavor matchSelectPattern(ICmpInst::Predicate Pred,
+ Value *CmpLHS, Value *CmpRHS,
+ Value *TrueVal, Value *FalseVal,
+ Value *&LHS, Value *&RHS) {
LHS = CmpLHS;
RHS = CmpRHS;
@@ -3300,3 +3290,55 @@ SelectPatternFlavor llvm::matchSelectPat
return SPF_UNKNOWN;
}
+
+static Constant *lookThroughCast(ICmpInst *CmpI, Value *V1, Value *V2,
+ Instruction::CastOps *CastOp) {
+ CastInst *CI = dyn_cast<CastInst>(V1);
+ Constant *C = dyn_cast<Constant>(V2);
+ if (!CI || !C)
+ return nullptr;
+ *CastOp = CI->getOpcode();
+
+ if ((isa<SExtInst>(CI) && CmpI->isSigned()) ||
+ (isa<ZExtInst>(CI) && CmpI->isUnsigned()))
+ return ConstantExpr::getTrunc(C, CI->getSrcTy());
+
+ if (isa<TruncInst>(CI))
+ return ConstantExpr::getIntegerCast(C, CI->getSrcTy(), CmpI->isSigned());
+
+ return nullptr;
+}
+
+SelectPatternFlavor llvm::matchSelectPattern(Value *V,
+ Value *&LHS, Value *&RHS,
+ Instruction::CastOps *CastOp) {
+ SelectInst *SI = dyn_cast<SelectInst>(V);
+ if (!SI) return SPF_UNKNOWN;
+
+ ICmpInst *CmpI = dyn_cast<ICmpInst>(SI->getCondition());
+ if (!CmpI) return SPF_UNKNOWN;
+
+ ICmpInst::Predicate Pred = CmpI->getPredicate();
+ Value *CmpLHS = CmpI->getOperand(0);
+ Value *CmpRHS = CmpI->getOperand(1);
+ Value *TrueVal = SI->getTrueValue();
+ Value *FalseVal = SI->getFalseValue();
+
+ // Bail out early.
+ if (CmpI->isEquality())
+ return SPF_UNKNOWN;
+
+ // Deal with type mismatches.
+ if (CastOp && CmpLHS->getType() != TrueVal->getType()) {
+ if (Constant *C = lookThroughCast(CmpI, TrueVal, FalseVal, CastOp))
+ return ::matchSelectPattern(Pred, CmpLHS, CmpRHS,
+ cast<CastInst>(TrueVal)->getOperand(0), C,
+ LHS, RHS);
+ if (Constant *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp))
+ return ::matchSelectPattern(Pred, CmpLHS, CmpRHS,
+ C, cast<CastInst>(FalseVal)->getOperand(0),
+ LHS, RHS);
+ }
+ return ::matchSelectPattern(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal,
+ LHS, RHS);
+}
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