[llvm-branch-commits] [llvm] f62b50e - [ValueTracking] Skip incoming values that are the same as the phi in `isGuaranteedNotToBeUndefOrPoison` (#130111)

[Tom Stellard via llvm-branch-commits]

Author: DianQK
Date: 2025-03-11T17:09:10-07:00
New Revision: f62b50e0e8f170412c95d7c1263c46a400bbeba8

URL: https://github.com/llvm/llvm-project/commit/f62b50e0e8f170412c95d7c1263c46a400bbeba8
DIFF: https://github.com/llvm/llvm-project/commit/f62b50e0e8f170412c95d7c1263c46a400bbeba8.diff

LOG: [ValueTracking] Skip incoming values that are the same as the phi in `isGuaranteedNotToBeUndefOrPoison` (#130111)

Fixes (keep it open) #130110.

If the incoming value is PHI itself, we can skip this. If we can
guarantee that the other incoming values are neither undef nor poison,
then we can also guarantee that the value isn't either. If we cannot
guarantee that, it makes no sense in calculating it.

(cherry picked from commit 462eb7e28ef4507b16a4b45efb356bc6a3523615)

Added: 
    llvm/test/Analysis/ValueTracking/phi-self.ll

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 4e79f41df2eb9..02a48d35a74aa 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7777,6 +7777,8 @@ static bool isGuaranteedNotToBeUndefOrPoison(
       unsigned Num = PN->getNumIncomingValues();
       bool IsWellDefined = true;
       for (unsigned i = 0; i < Num; ++i) {
+        if (PN == PN->getIncomingValue(i))
+          continue;
         auto *TI = PN->getIncomingBlock(i)->getTerminator();
         if (!isGuaranteedNotToBeUndefOrPoison(PN->getIncomingValue(i), AC, TI,
                                               DT, Depth + 1, Kind)) {

diff  --git a/llvm/test/Analysis/ValueTracking/phi-self.ll b/llvm/test/Analysis/ValueTracking/phi-self.ll
new file mode 100644
index 0000000000000..17afd872cab03
--- /dev/null
+++ b/llvm/test/Analysis/ValueTracking/phi-self.ll
@@ -0,0 +1,89 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instsimplify < %s | FileCheck %s
+
+; Test `%r` can be replaced by `%nonpoison`.
+
+define i32 @other_noundef(i32 noundef %arg) {
+; CHECK-LABEL: define i32 @other_noundef(
+; CHECK-SAME: i32 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  [[START:.*]]:
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[NONPOISON:%.*]] = phi i32 [ 0, %[[START]] ], [ [[NONPOISON]], %[[BB0:.*]] ], [ [[ARG]], %[[BB1:.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = call i32 @opaque()
+; CHECK-NEXT:    switch i32 [[I]], label %[[EXIT:.*]] [
+; CHECK-NEXT:      i32 0, label %[[BB0]]
+; CHECK-NEXT:      i32 1, label %[[BB1]]
+; CHECK-NEXT:    ]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret i32 [[NONPOISON]]
+; CHECK:       [[BB0]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+;
+start:
+  br label %loop
+
+loop:
+  %nonpoison = phi i32 [ 0, %start ], [ %nonpoison, %bb0 ], [ %arg, %bb1 ]
+  %i = call i32 @opaque()
+  switch i32 %i, label %exit [
+  i32 0, label %bb0
+  i32 1, label %bb1
+  ]
+
+exit:
+  %r = freeze i32 %nonpoison
+  ret i32 %r
+
+bb0:
+  br label %loop
+
+bb1:
+  br label %loop
+}
+
+define i32 @other_poison(i32 %arg) {
+; CHECK-LABEL: define i32 @other_poison(
+; CHECK-SAME: i32 [[ARG:%.*]]) {
+; CHECK-NEXT:  [[START:.*]]:
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[MAYPOISON:%.*]] = phi i32 [ 0, %[[START]] ], [ [[MAYPOISON]], %[[BB0:.*]] ], [ [[ARG]], %[[BB1:.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = call i32 @opaque()
+; CHECK-NEXT:    switch i32 [[I]], label %[[EXIT:.*]] [
+; CHECK-NEXT:      i32 0, label %[[BB0]]
+; CHECK-NEXT:      i32 1, label %[[BB1]]
+; CHECK-NEXT:    ]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    [[R:%.*]] = freeze i32 [[MAYPOISON]]
+; CHECK-NEXT:    ret i32 [[R]]
+; CHECK:       [[BB0]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+;
+start:
+  br label %loop
+
+loop:
+  %maypoison = phi i32 [ 0, %start ], [ %maypoison, %bb0 ], [ %arg, %bb1 ]
+  %i = call i32 @opaque()
+  switch i32 %i, label %exit [
+  i32 0, label %bb0
+  i32 1, label %bb1
+  ]
+
+exit:
+  %r = freeze i32 %maypoison
+  ret i32 %r
+
+bb0:
+  br label %loop
+
+bb1:
+  br label %loop
+}
+
+declare i32 @opaque()