[PATCH] D103834: [SCEV] Properly guard reasoning about infinite loops being UB on mustprogress

[Philip Reames 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 rG3c6e419198f3: [SCEV] Properly guard reasoning about infinite loops being UB on mustprogress (authored by reames).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103834/new/

https://reviews.llvm.org/D103834

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
  llvm/test/Transforms/LoopVectorize/pr38697.ll


Index: llvm/test/Transforms/LoopVectorize/pr38697.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/pr38697.ll
+++ llvm/test/Transforms/LoopVectorize/pr38697.ll
@@ -30,7 +30,7 @@
 
 ; Verify that a 'udiv' does not appear in the 'loop1.preheader' block, and that
 ; a 'udiv' has been inserted at the top of the 'while.body.preheader' block.
-define void @testCountIncrLoop(i8* %ptr, i32 %lim, i32 %count, i32 %val) {
+define void @testCountIncrLoop(i8* %ptr, i32 %lim, i32 %count, i32 %val) mustprogress {
 ; CHECK-LABEL: @testCountIncrLoop(
 ; CHECK-NEXT:  entry:
 ; CHECK:       loop1.preheader:
Index: llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
+++ llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
@@ -13,8 +13,7 @@
 
 target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
 
-; Function Attrs: norecurse nounwind
-define void @foo1(i32* nocapture %A, i32 %n, i32 %s) #0 {
+define void @foo1(i32* nocapture %A, i32 %n, i32 %s) mustprogress {
 entry:
   %cmp4 = icmp sgt i32 %n, 0
   br i1 %cmp4, label %for.body, label %for.end
@@ -42,8 +41,7 @@
 ; loops with unknown stride.
 ; CHECK: max backedge-taken count is -1
 
-; Function Attrs: norecurse nounwind
-define void @foo2(i32* nocapture %A, i32 %n, i32 %s) #0 {
+define void @foo2(i32* nocapture %A, i32 %n, i32 %s) mustprogress {
 entry:
   br label %for.body
 
@@ -61,3 +59,26 @@
   ret void
 }
 
+; Check that without mustprogress we don't make assumptions about infinite
+; loops being UB.
+; CHECK: Determining loop execution counts for: @foo3
+; CHECK: Loop %for.body: Unpredictable backedge-taken count.
+; CHECK: Loop %for.body: Unpredictable max backedge-taken count.
+
+define void @foo3(i32* nocapture %A, i32 %n, i32 %s) {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %i.05 = phi i32 [ %add, %for.body ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32, i32* %A, i32 %i.05
+  %0 = load i32, i32* %arrayidx, align 4
+  %inc = add nsw i32 %0, 1
+  store i32 %inc, i32* %arrayidx, align 4
+  %add = add nsw i32 %i.05, %s
+  %cmp = icmp slt i32 %add, %n
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:                                          ; preds = %for.body, %entry
+  ret void
+}
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -11470,7 +11470,7 @@
     //   A[i] = i;
     //
     if (PredicatedIV || !NoWrap || isKnownNonPositive(Stride) ||
-        !loopHasNoSideEffects(L))
+        !loopIsFiniteByAssumption(L))
       return getCouldNotCompute();
   } else if (!Stride->isOne() && !NoWrap) {
     auto isUBOnWrap = [&]() {


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