[PATCH] D141114: [LoopFlattening] Check for extra uses on Mul

[Dave Green via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG161bfa5f53ef: [LoopFlattening] Check for extra uses on Mul (authored by dmgreen).

Changed prior to commit:
  https://reviews.llvm.org/D141114?vs=486767&id=486878#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D141114/new/

https://reviews.llvm.org/D141114

Files:
  llvm/lib/Transforms/Scalar/LoopFlatten.cpp
  llvm/test/Transforms/LoopFlatten/pr59339.ll


Index: llvm/test/Transforms/LoopFlatten/pr59339.ll
===================================================================
--- llvm/test/Transforms/LoopFlatten/pr59339.ll
+++ llvm/test/Transforms/LoopFlatten/pr59339.ll
@@ -1,14 +1,11 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -S -opaque-pointers -passes='loop(loop-flatten),verify' -verify-loop-info -verify-dom-info -verify-scev | FileCheck %s
 
-; FIXME: This incorrectly triggers, thus resulting in a miscompilation.
-; The problem is that there is a linear use of the induction variable, i*3+j,
-; but only the part i*3 is used for indexing.
+; Check that the mul does not have extra uses.
 
 define void @test0(ptr %arg, ptr %arg1) {
 ; CHECK-LABEL: @test0(
 ; CHECK-NEXT:  bb:
-; CHECK-NEXT:    [[FLATTEN_TRIPCOUNT:%.*]] = mul i64 3, 2
 ; CHECK-NEXT:    br label [[DOTPREHEADER:%.*]]
 ; CHECK:       .preheader:
 ; CHECK-NEXT:    [[I:%.*]] = phi i64 [ 0, [[BB:%.*]] ], [ [[I5:%.*]], [[BB4:%.*]] ]
@@ -17,17 +14,17 @@
 ; CHECK-NEXT:    br label [[BB7:%.*]]
 ; CHECK:       bb4:
 ; CHECK-NEXT:    [[I5]] = add i64 [[I]], 1
-; CHECK-NEXT:    [[I6:%.*]] = icmp slt i64 [[I5]], [[FLATTEN_TRIPCOUNT]]
+; CHECK-NEXT:    [[I6:%.*]] = icmp slt i64 [[I5]], 2
 ; CHECK-NEXT:    br i1 [[I6]], label [[DOTPREHEADER]], label [[BB14:%.*]]
 ; CHECK:       bb7:
-; CHECK-NEXT:    [[I8:%.*]] = phi i64 [ 0, [[DOTPREHEADER]] ]
+; CHECK-NEXT:    [[I8:%.*]] = phi i64 [ 0, [[DOTPREHEADER]] ], [ [[I12:%.*]], [[BB7]] ]
 ; CHECK-NEXT:    [[I9:%.*]] = load i16, ptr [[I3]], align 2
 ; CHECK-NEXT:    [[I10:%.*]] = add i64 [[I8]], [[I2]]
-; CHECK-NEXT:    [[I11:%.*]] = getelementptr i16, ptr [[ARG:%.*]], i64 [[I]]
+; CHECK-NEXT:    [[I11:%.*]] = getelementptr i16, ptr [[ARG:%.*]], i64 [[I10]]
 ; CHECK-NEXT:    store i16 [[I9]], ptr [[I11]], align 2
-; CHECK-NEXT:    [[I12:%.*]] = add nuw nsw i64 [[I8]], 1
+; CHECK-NEXT:    [[I12]] = add nuw nsw i64 [[I8]], 1
 ; CHECK-NEXT:    [[I13:%.*]] = icmp ult i64 [[I12]], 3
-; CHECK-NEXT:    br label [[BB4]]
+; CHECK-NEXT:    br i1 [[I13]], label [[BB7]], label [[BB4]]
 ; CHECK:       bb14:
 ; CHECK-NEXT:    ret void
 ;
Index: llvm/lib/Transforms/Scalar/LoopFlatten.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopFlatten.cpp
+++ llvm/lib/Transforms/Scalar/LoopFlatten.cpp
@@ -215,6 +215,15 @@
     LLVM_DEBUG(dbgs() << "Matched multiplication: "; MatchedMul->dump());
     LLVM_DEBUG(dbgs() << "Matched iteration count: "; MatchedItCount->dump());
 
+    // The mul should not have any other uses. Widening may leave trivially dead
+    // uses, which can be ignored.
+    if (count_if(MatchedMul->users(), [](User *U) {
+          return !isInstructionTriviallyDead(cast<Instruction>(U));
+        }) > 1) {
+      LLVM_DEBUG(dbgs() << "Multiply has more than one use\n");
+      return false;
+    }
+
     // Look through extends if the IV has been widened. Don't look through
     // extends if we already looked through a trunc.
     if (Widened && IsAdd &&


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