[llvm] r255504 - [InstCombine] fold trunc ([lshr] (bitcast vector) ) --> extractelement (PR25543)
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Dec 14 08:16:54 PST 2015
Author: spatel
Date: Mon Dec 14 10:16:54 2015
New Revision: 255504
URL: http://llvm.org/viewvc/llvm-project?rev=255504&view=rev
Log:
[InstCombine] fold trunc ([lshr] (bitcast vector) ) --> extractelement (PR25543)
This is a fix for PR25543:
https://llvm.org/bugs/show_bug.cgi?id=25543
The idea is to take the existing fold of:
bitcast ( trunc ( lshr ( bitcast X))) --> extractelement (bitcast X)
( http://reviews.llvm.org/rL112232 )
And break it into less specific transforms so we'll catch more cases such as
the example in the bug report:
bitcast ( trunc ( lshr ( bitcast X))) -->
bitcast ( extractelement (bitcast X)) -->
extractelement (bitcast X)
Enabling patches for this change:
http://reviews.llvm.org/rL255399 (combine bitcasts)
http://reviews.llvm.org/rL255433 (canonicalize extractelement(bitcast X))
Differential Revision: http://reviews.llvm.org/D15392
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
llvm/trunk/test/Transforms/InstCombine/trunc.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=255504&r1=255503&r2=255504&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Mon Dec 14 10:16:54 2015
@@ -430,6 +430,50 @@ static bool canEvaluateTruncated(Value *
return false;
}
+/// Given a vector that is bitcast to an integer, optionally logically
+/// right-shifted, and truncated, convert it to an extractelement.
+/// Example (big endian):
+/// trunc (lshr (bitcast <4 x i32> %X to i128), 32) to i32
+/// --->
+/// extractelement <4 x i32> %X, 1
+static Instruction *foldVecTruncToExtElt(TruncInst &Trunc, InstCombiner &IC,
+ const DataLayout &DL) {
+ Value *TruncOp = Trunc.getOperand(0);
+ Type *DestType = Trunc.getType();
+ if (!TruncOp->hasOneUse() || !isa<IntegerType>(DestType))
+ return nullptr;
+
+ Value *VecInput = nullptr;
+ ConstantInt *ShiftVal = nullptr;
+ if (!match(TruncOp, m_CombineOr(m_BitCast(m_Value(VecInput)),
+ m_LShr(m_BitCast(m_Value(VecInput)),
+ m_ConstantInt(ShiftVal)))) ||
+ !isa<VectorType>(VecInput->getType()))
+ return nullptr;
+
+ VectorType *VecType = cast<VectorType>(VecInput->getType());
+ unsigned VecWidth = VecType->getPrimitiveSizeInBits();
+ unsigned DestWidth = DestType->getPrimitiveSizeInBits();
+ unsigned ShiftAmount = ShiftVal ? ShiftVal->getZExtValue() : 0;
+
+ if ((VecWidth % DestWidth != 0) || (ShiftAmount % DestWidth != 0))
+ return nullptr;
+
+ // If the element type of the vector doesn't match the result type,
+ // bitcast it to a vector type that we can extract from.
+ unsigned NumVecElts = VecWidth / DestWidth;
+ if (VecType->getElementType() != DestType) {
+ VecType = VectorType::get(DestType, NumVecElts);
+ VecInput = IC.Builder->CreateBitCast(VecInput, VecType, "bc");
+ }
+
+ unsigned Elt = ShiftAmount / DestWidth;
+ if (DL.isBigEndian())
+ Elt = NumVecElts - 1 - Elt;
+
+ return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
+}
+
Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
if (Instruction *Result = commonCastTransforms(CI))
return Result;
@@ -528,6 +572,9 @@ Instruction *InstCombiner::visitTrunc(Tr
ConstantExpr::getTrunc(Cst, DestTy));
}
+ if (Instruction *I = foldVecTruncToExtElt(CI, *this, DL))
+ return I;
+
return nullptr;
}
@@ -1740,56 +1787,6 @@ static Instruction *canonicalizeBitCastE
return ExtractElementInst::Create(NewBC, ExtElt->getIndexOperand());
}
-static Instruction *foldVecTruncToExtElt(Value *VecInput, Type *DestTy,
- unsigned ShiftAmt, InstCombiner &IC,
- const DataLayout &DL) {
- VectorType *VecTy = cast<VectorType>(VecInput->getType());
- unsigned DestWidth = DestTy->getPrimitiveSizeInBits();
- unsigned VecWidth = VecTy->getPrimitiveSizeInBits();
-
- if ((VecWidth % DestWidth != 0) || (ShiftAmt % DestWidth != 0))
- return nullptr;
-
- // If the element type of the vector doesn't match the result type,
- // bitcast it to be a vector type we can extract from.
- unsigned NumVecElts = VecWidth / DestWidth;
- if (VecTy->getElementType() != DestTy) {
- VecTy = VectorType::get(DestTy, NumVecElts);
- VecInput = IC.Builder->CreateBitCast(VecInput, VecTy);
- }
-
- unsigned Elt = ShiftAmt / DestWidth;
- if (DL.isBigEndian())
- Elt = NumVecElts - 1 - Elt;
-
- return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
-}
-
-/// See if we can optimize an integer->float/double bitcast.
-/// The various long double bitcasts can't get in here.
-static Instruction *optimizeIntToFloatBitCast(BitCastInst &CI, InstCombiner &IC,
- const DataLayout &DL) {
- Value *Src = CI.getOperand(0);
- Type *DstTy = CI.getType();
-
- // If this is a bitcast from int to float, check to see if the int is an
- // extraction from a vector.
- Value *VecInput = nullptr;
- // bitcast(trunc(bitcast(somevector)))
- if (match(Src, m_Trunc(m_BitCast(m_Value(VecInput)))) &&
- isa<VectorType>(VecInput->getType()))
- return foldVecTruncToExtElt(VecInput, DstTy, 0, IC, DL);
-
- // bitcast(trunc(lshr(bitcast(somevector), cst))
- ConstantInt *ShAmt = nullptr;
- if (match(Src, m_Trunc(m_LShr(m_BitCast(m_Value(VecInput)),
- m_ConstantInt(ShAmt)))) &&
- isa<VectorType>(VecInput->getType()))
- return foldVecTruncToExtElt(VecInput, DstTy, ShAmt->getZExtValue(), IC, DL);
-
- return nullptr;
-}
-
Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
// If the operands are integer typed then apply the integer transforms,
// otherwise just apply the common ones.
@@ -1833,11 +1830,6 @@ Instruction *InstCombiner::visitBitCast(
}
}
- // Try to optimize int -> float bitcasts.
- if ((DestTy->isFloatTy() || DestTy->isDoubleTy()) && isa<IntegerType>(SrcTy))
- if (Instruction *I = optimizeIntToFloatBitCast(CI, *this, DL))
- return I;
-
if (VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
if (DestVTy->getNumElements() == 1 && !SrcTy->isVectorTy()) {
Value *Elem = Builder->CreateBitCast(Src, DestVTy->getElementType());
Modified: llvm/trunk/test/Transforms/InstCombine/trunc.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/trunc.ll?rev=255504&r1=255503&r2=255504&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/trunc.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/trunc.ll Mon Dec 14 10:16:54 2015
@@ -121,7 +121,7 @@ define i8 @test10(i32 %X) {
; PR25543
; https://llvm.org/bugs/show_bug.cgi?id=25543
-; TODO: This could be extractelement.
+; This is an extractelement.
define i32 @trunc_bitcast1(<4 x i32> %v) {
%bc = bitcast <4 x i32> %v to i128
@@ -130,13 +130,11 @@ define i32 @trunc_bitcast1(<4 x i32> %v)
ret i32 %ext
; CHECK-LABEL: @trunc_bitcast1(
-; CHECK-NEXT: %bc = bitcast <4 x i32> %v to i128
-; CHECK-NEXT: %shr = lshr i128 %bc, 32
-; CHECK-NEXT: %ext = trunc i128 %shr to i32
+; CHECK-NEXT: %ext = extractelement <4 x i32> %v, i32 1
; CHECK-NEXT: ret i32 %ext
}
-; TODO: This could be bitcast + extractelement.
+; A bitcast may still be required.
define i32 @trunc_bitcast2(<2 x i64> %v) {
%bc = bitcast <2 x i64> %v to i128
@@ -145,13 +143,12 @@ define i32 @trunc_bitcast2(<2 x i64> %v)
ret i32 %ext
; CHECK-LABEL: @trunc_bitcast2(
-; CHECK-NEXT: %bc = bitcast <2 x i64> %v to i128
-; CHECK-NEXT: %shr = lshr i128 %bc, 64
-; CHECK-NEXT: %ext = trunc i128 %shr to i32
+; CHECK-NEXT: %bc1 = bitcast <2 x i64> %v to <4 x i32>
+; CHECK-NEXT: %ext = extractelement <4 x i32> %bc1, i32 2
; CHECK-NEXT: ret i32 %ext
}
-; TODO: The shift is optional. This could be extractelement.
+; The right shift is optional.
define i32 @trunc_bitcast3(<4 x i32> %v) {
%bc = bitcast <4 x i32> %v to i128
@@ -159,8 +156,7 @@ define i32 @trunc_bitcast3(<4 x i32> %v)
ret i32 %ext
; CHECK-LABEL: @trunc_bitcast3(
-; CHECK-NEXT: %bc = bitcast <4 x i32> %v to i128
-; CHECK-NEXT: %ext = trunc i128 %bc to i32
+; CHECK-NEXT: %ext = extractelement <4 x i32> %v, i32 0
; CHECK-NEXT: ret i32 %ext
}
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