[llvm] [LV] Only check isVectorizableEarlyExitLoop with multiple exits. (PR #121994)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-vectorizers

Author: Florian Hahn (fhahn)

<details>
<summary>Changes</summary>

Currently we emit early-exit related debug messages/remarks even when there is a single exit. Update to only check isVectorizableEarlyExitLoop if there isn't a single exit block.

---
Full diff: https://github.com/llvm/llvm-project/pull/121994.diff


4 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp (+13-4) 
- (modified) llvm/test/Transforms/LoopVectorize/X86/vectorization-remarks-missed.ll (+5-5) 
- (modified) llvm/test/Transforms/LoopVectorize/early_exit_legality.ll (+1-1) 
- (modified) llvm/test/Transforms/LoopVectorize/uncountable-single-exit-loops.ll (+3-3) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index cb0b4641b6492b..b11406bb0f390b 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -1784,14 +1784,23 @@ bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) {
 
   HasUncountableEarlyExit = false;
   if (isa<SCEVCouldNotCompute>(PSE.getBackedgeTakenCount())) {
-    HasUncountableEarlyExit = true;
-    if (!isVectorizableEarlyExitLoop()) {
-      UncountableExitingBlocks.clear();
-      HasUncountableEarlyExit = false;
+    if (TheLoop->getExitingBlock()) {
+      reportVectorizationFailure("Cannot vectorize uncountable loop",
+                                 "UnsupportedUncountableLoop", ORE, TheLoop);
       if (DoExtraAnalysis)
         Result = false;
       else
         return false;
+    } else {
+      HasUncountableEarlyExit = true;
+      if (!isVectorizableEarlyExitLoop()) {
+        UncountableExitingBlocks.clear();
+        HasUncountableEarlyExit = false;
+        if (DoExtraAnalysis)
+          Result = false;
+        else
+          return false;
+      }
     }
   }
 
diff --git a/llvm/test/Transforms/LoopVectorize/X86/vectorization-remarks-missed.ll b/llvm/test/Transforms/LoopVectorize/X86/vectorization-remarks-missed.ll
index 4c0317e300f190..70134fa6bc78d6 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/vectorization-remarks-missed.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/vectorization-remarks-missed.ll
@@ -12,7 +12,7 @@
 ;   }
 ; }
 ; File, line, and column should match those specified in the metadata
-; CHECK: remark: source.cpp:5:9: loop not vectorized: Cannot vectorize early exit loop
+; CHECK: remark: source.cpp:5:9: loop not vectorized: Cannot vectorize uncountable loop
 ; CHECK: remark: source.cpp:5:9: loop not vectorized
 
 ; void test_disabled(int *A, int Length) {
@@ -46,12 +46,12 @@
 
 ; YAML:       --- !Analysis
 ; YAML-NEXT: Pass:            loop-vectorize
-; YAML-NEXT: Name:            EarlyExitNotLatchPredecessor
+; YAML-NEXT: Name:            UnsupportedUncountableLoop
 ; YAML-NEXT: DebugLoc:        { File: source.cpp, Line: 5, Column: 9 }
 ; YAML-NEXT: Function:        _Z4testPii
 ; YAML-NEXT: Args:
 ; YAML-NEXT:   - String:          'loop not vectorized: '
-; YAML-NEXT:   - String:          Cannot vectorize early exit loop
+; YAML-NEXT:   - String:          Cannot vectorize uncountable loop
 ; YAML-NEXT: ...
 ; YAML-NEXT: --- !Missed
 ; YAML-NEXT: Pass:            loop-vectorize
@@ -117,12 +117,12 @@
 ; YAML-NEXT: ...
 ; YAML-NEXT: --- !Analysis
 ; YAML-NEXT: Pass:            loop-vectorize
-; YAML-NEXT: Name:            EarlyExitNotLatchPredecessor
+; YAML-NEXT: Name:            UnsupportedUncountableLoop
 ; YAML-NEXT: DebugLoc:        { File: source.cpp, Line: 27, Column: 3 }
 ; YAML-NEXT: Function:        test_multiple_failures
 ; YAML-NEXT: Args:
 ; YAML-NEXT:   - String:          'loop not vectorized: '
-; YAML-NEXT:   - String:          Cannot vectorize early exit loop
+; YAML-NEXT:   - String:          Cannot vectorize uncountable loop
 ; YAML-NEXT: ...
 ; YAML:      --- !Missed
 ; YAML-NEXT: Pass:            loop-vectorize
diff --git a/llvm/test/Transforms/LoopVectorize/early_exit_legality.ll b/llvm/test/Transforms/LoopVectorize/early_exit_legality.ll
index 8df0eaec6a8c9d..6d365b9d77e80b 100644
--- a/llvm/test/Transforms/LoopVectorize/early_exit_legality.ll
+++ b/llvm/test/Transforms/LoopVectorize/early_exit_legality.ll
@@ -357,7 +357,7 @@ loop.end:
 
 define i64 @uncountable_exit_infinite_loop() {
 ; CHECK-LABEL: LV: Checking a loop in 'uncountable_exit_infinite_loop'
-; CHECK:       LV: Not vectorizing: Cannot determine exact exit count for latch block.
+; CHECK:       LV: Not vectorizing: Cannot vectorize uncountable loop.
 entry:
   %p1 = alloca [1024 x i8]
   %p2 = alloca [1024 x i8]
diff --git a/llvm/test/Transforms/LoopVectorize/uncountable-single-exit-loops.ll b/llvm/test/Transforms/LoopVectorize/uncountable-single-exit-loops.ll
index 252061335e7365..c3958262f0af89 100644
--- a/llvm/test/Transforms/LoopVectorize/uncountable-single-exit-loops.ll
+++ b/llvm/test/Transforms/LoopVectorize/uncountable-single-exit-loops.ll
@@ -1,17 +1,17 @@
 ; REQUIRES: asserts
-; RUN: opt -p loop-vectorize -debug %s 2>&1 | FileCheck %s
+; RUN: opt -p loop-vectorize -debug-only=loop-vectorize -S %s 2>&1 | FileCheck %s
 
 
 ; CHECK-LABEL: LV: Checking a loop in 'latch_exit_cannot_compute_btc_due_to_step'
 ; CHECK: 	   LV: Did not find one integer induction var.
-; CHECK-NEXT:  LV: Not vectorizing: Early exit is not the latch predecessor.
+; CHECK-NEXT:  LV: Not vectorizing: Cannot vectorize uncountable loop.
 ; CHECK-NEXT:  LV: Interleaving disabled by the pass manager
 ; CHECK-NEXT:  LV: Not vectorizing: Cannot prove legality.
 
 ; CHECK-LABEL: LV: Checking a loop in 'header_exit_cannot_compute_btc_due_to_step'
 ; CHECK:       LV: Found an induction variable.
 ; CHECK-NEXT:  LV: Did not find one integer induction var.
-; CHECK-NEXT:  LV: Not vectorizing: Cannot determine exact exit count for latch block.
+; CHECK-NEXT:  LV: Not vectorizing: Cannot vectorize uncountable loop.
 ; CHECK-NEXT:  LV: Interleaving disabled by the pass manager
 ; CHECK-NEXT:  LV: Not vectorizing: Cannot prove legality.
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/121994