maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[ValueTracking] Teach computeKnownBits and ComputeNumSignBits to look through ExtractElement. 

Summary:
The computeKnownBits and ComputeNumSignBits functions in ValueTracking can now do a simple look-through of ExtractElement.

Reviewers: majnemer, spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D24955

llvm-svn: 283434
This commit is contained in:
Bjorn Pettersson 2016-10-06 09:56:21 +00:00
parent f9292220dc
commit 3961603921
2 changed files with 42 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -1389,6 +1389,13 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
}
}
break;
case Instruction::ExtractElement:
// Look through extract element. At the moment we keep this simple and skip
// tracking the specific element. But at least we might find information
// valid for all elements of the vector (for example if vector is sign
// extended, shifted, etc).
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
break;
case Instruction::ExtractValue:
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) {
const ExtractValueInst *EVI = cast<ExtractValueInst>(I);
@ -2220,6 +2227,13 @@ unsigned ComputeNumSignBits(const Value *V, unsigned Depth, const Query &Q) {
// FIXME: it's tricky to do anything useful for this, but it is an important
// case for targets like X86.
break;
case Instruction::ExtractElement:
// Look through extract element. At the moment we keep this simple and skip
// tracking the specific element. But at least we might find information
// valid for all elements of the vector (for example if vector is sign
// extended, shifted, etc).
return ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
}
// Finally, if we can prove that the top bits of the result are 0's or 1's,

28
llvm/test/Analysis/ValueTracking/signbits-extract-elt.ll Normal file
View File

@ -0,0 +1,28 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -instsimplify -S | FileCheck %s
; If computeKnownBits can do a simple look-through for extractelement
; then instsimplify will know that %elt1 is non-negative at icmp.
define i1 @computeKnownBits_look_through_extractelt(<2 x i8> %vecin) {
; CHECK-LABEL: @computeKnownBits_look_through_extractelt(
; CHECK-NEXT: ret i1 false
;
%vec = zext <2 x i8> %vecin to <2 x i32>
%elt1 = extractelement <2 x i32> %vec, i32 1
%bool = icmp slt i32 %elt1, 0
ret i1 %bool
}
; If computeNumSignBits can do a simple look-through for extractelement
; then instsimplify will remove the ashr.
define i32 @computeNumSignBits_look_through_extractelt(<2 x i1> %vecin) {
; CHECK-LABEL: @computeNumSignBits_look_through_extractelt(
; CHECK-NEXT: [[VEC:%.*]] = sext <2 x i1> [[VEC:%.*]]in to <2 x i32>
; CHECK-NEXT: [[ELT0:%.*]] = extractelement <2 x i32> [[VEC]], i32 0
; CHECK-NEXT: ret i32 [[ELT0]]
;
%vec = sext <2 x i1> %vecin to <2 x i32>
%elt0 = extractelement <2 x i32> %vec, i32 0
%ashr = ashr i32 %elt0, 5
ret i32 %ashr
}