[PATCH] D24955: [ValueTracking] Teach computeKnownBits and ComputeNumSignBits to look through ExtractElement.
Bjorn Pettersson via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 28 05:07:29 PDT 2016
bjope updated this revision to Diff 72804.
bjope added a comment.
Updated accoring to recommendations from Sanjay.
https://reviews.llvm.org/D24955
Files:
lib/Analysis/ValueTracking.cpp
test/Analysis/ValueTracking/signbits-extract-elt.ll
Index: test/Analysis/ValueTracking/signbits-extract-elt.ll
===================================================================
--- /dev/null
+++ test/Analysis/ValueTracking/signbits-extract-elt.ll
@@ -0,0 +1,25 @@
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+
+; If computeKnownBits can do a simple look-through for extractelement
+; then instsimplify will now 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> %vecin 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
+}
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1389,6 +1389,13 @@
}
}
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 @@
// 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,
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