From c3ffe9191ab91b84a106dcf75e55c5ac0bfe5f57 Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Mon, 30 Mar 2020 11:17:57 -0400
Subject: [PATCH] Backport of part of D71181.
This backports *just* the bug fix portion of
https://github.com/llvm/llvm-project/commit/a7d992c0f2d235c67f04160405c5c5606408d4b1#diff-1f9547b463bf33c1dd86f485d0fa410eR1465
---
llvm/lib/Analysis/InstructionSimplify.cpp | 10 +++++++--
llvm/lib/Analysis/ValueTracking.cpp | 27 +++++++++++++++++++----
2 files changed, 31 insertions(+), 6 deletions(-)
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 941a68c5e6fd8..3ea6b9e0c235b 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -543,10 +543,16 @@ static Value *ThreadCmpOverPHI(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
// Evaluate the BinOp on the incoming phi values.
Value *CommonValue = nullptr;
- for (Value *Incoming : PI->incoming_values()) {
+ for (unsigned u = 0, e = PI->getNumIncomingValues(); u < e; ++u) {
+ Value *Incoming = PI->getIncomingValue(u);
+ Instruction *InTI = PI->getIncomingBlock(u)->getTerminator();
// If the incoming value is the phi node itself, it can safely be skipped.
if (Incoming == PI) continue;
- Value *V = SimplifyCmpInst(Pred, Incoming, RHS, Q, MaxRecurse);
+ // Change the context instruction to the "edge" that flows into the phi.
+ // This is important because that is where incoming is actually "evaluated"
+ // even though it is used later somewhere else.
+ Value *V = SimplifyCmpInst(Pred, Incoming, RHS, Q.getWithInstruction(InTI),
+ MaxRecurse);
// If the operation failed to simplify, or simplified to a different value
// to previously, then give up.
if (!V || (CommonValue && V != CommonValue))
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index c70906dcc6295..b2874bb138935 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1346,6 +1346,8 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
for (unsigned i = 0; i != 2; ++i) {
Value *L = P->getIncomingValue(i);
Value *R = P->getIncomingValue(!i);
+ Instruction *RInst = P->getIncomingBlock(!i)->getTerminator();
+ Instruction *LInst = P->getIncomingBlock(i)->getTerminator();
Operator *LU = dyn_cast<Operator>(L);
if (!LU)
continue;
@@ -1367,13 +1369,22 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
L = LL;
else
break;
+
+ // Change the context instruction to the "edge" that flows into the
+ // phi. This is important because that is where the value is actually
+ // "evaluated" even though it is used later somewhere else. (see also
+ // D69571).
+ Query RecQ = Q;
+
// Ok, we have a PHI of the form L op= R. Check for low
// zero bits.
- computeKnownBits(R, Known2, Depth + 1, Q);
+ RecQ.CxtI = RInst;
+ computeKnownBits(R, Known2, Depth + 1, RecQ);
// We need to take the minimum number of known bits
KnownBits Known3(Known);
- computeKnownBits(L, Known3, Depth + 1, Q);
+ RecQ.CxtI = LInst;
+ computeKnownBits(L, Known3, Depth + 1, RecQ);
Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(),
Known3.countMinTrailingZeros()));
@@ -1429,14 +1440,22 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
Known.Zero.setAllBits();
Known.One.setAllBits();
- for (Value *IncValue : P->incoming_values()) {
+ for (unsigned u = 0, e = P->getNumIncomingValues(); u < e; ++u) {
+ Value *IncValue = P->getIncomingValue(u);
// Skip direct self references.
if (IncValue == P) continue;
+ // Change the context instruction to the "edge" that flows into the
+ // phi. This is important because that is where the value is actually
+ // "evaluated" even though it is used later somewhere else. (see also
+ // D69571).
+ Query RecQ = Q;
+ RecQ.CxtI = P->getIncomingBlock(u)->getTerminator();
+
Known2 = KnownBits(BitWidth);
// Recurse, but cap the recursion to one level, because we don't
// want to waste time spinning around in loops.
- computeKnownBits(IncValue, Known2, MaxDepth - 1, Q);
+ computeKnownBits(IncValue, Known2, MaxDepth - 1, RecQ);
Known.Zero &= Known2.Zero;
Known.One &= Known2.One;
// If all bits have been ruled out, there's no need to check