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

Noticed via code inspection. We changed the semantics of the IR when we added mustprogress, and we appear to have not updated this location.

Differential Revision: https://reviews.llvm.org/D103834

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 273b2ec632202000f79b679e39fc9a78edc91afb..57a6c83ddd46b8191ad2f24fffe0ea30b03bea85 100644 (file)
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -11470,7 +11470,7 @@ ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
     //   A[i] = i;
     //
     if (PredicatedIV || !NoWrap || isKnownNonPositive(Stride) ||
-        !loopHasNoSideEffects(L))
+        !loopIsFiniteByAssumption(L))
       return getCouldNotCompute();
   } else if (!Stride->isOne() && !NoWrap) {
     auto isUBOnWrap = [&]() {

diff --git a/llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll b/llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
index fa9c7832adbe374d1120cccc5c37a134e1fc6e16..7d41a1f3e54626f8f07c6fc9e2e810451453c5c0 100644 (file)
--- a/llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
+++ b/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 @@ for.end:                                          ; preds = %for.body, %entry
 ; 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 @@ for.end:                                          ; preds = %for.body, %entry
   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
+}

diff --git a/llvm/test/Transforms/LoopVectorize/pr38697.ll b/llvm/test/Transforms/LoopVectorize/pr38697.ll
index 72b698613c6e9d59b4369a676d452db045e9721e..69dcdb08ece69c8053f79dc3f97d36ac4bccf3a5 100644 (file)
--- a/llvm/test/Transforms/LoopVectorize/pr38697.ll
+++ b/llvm/test/Transforms/LoopVectorize/pr38697.ll
@@ -30,7 +30,7 @@ target triple = "x86_64-unknown-linux-gnu"
 
 ; 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: