[PATCH] D30719: AMDGPU/SI: Disable unrolling in the loop vectorizer if the loop is not vectorized.

[Changpeng Fang via Phabricator via llvm-commits]

cfang updated this revision to Diff 91049.
cfang added a comment.

Add a test case.

I was thinking that we should still be able to use the backend option: -force-target-max-scalar-interleave

But it seems the code in LoopVectorize.cpp prevents us doing this:

// Don't attempt if

  // 1. the target claims to have no vector registers, and
  // 2. interleaving won't help ILP.
  //
  // The second condition is necessary because, even if the target has no
  // vector registers, loop vectorization may still enable scalar
  // interleaving.
  if (!TTI->getNumberOfRegisters(true) && TTI->getMaxInterleaveFactor(1) < 2) {
    return false;
  }


https://reviews.llvm.org/D30719

Files:
  lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
  test/CodeGen/AMDGPU/unroll-in-loop-vectorizer.ll


Index: test/CodeGen/AMDGPU/unroll-in-loop-vectorizer.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/unroll-in-loop-vectorizer.ll
@@ -0,0 +1,29 @@
+; RUN: opt -S -mtriple=amdgcn-unknown-amdhsa -mcpu=fiji -loop-vectorize < %s | FileCheck %s
+
+
+; For AMDGPU, loop unroll in loop vectorizer is disabled when VF==1.
+;
+; CHECK-LABEL: @small_loop(
+; CHECK: store i32
+; CHECK-NOT: store i32
+; CHECK: ret
+define void @small_loop(i32* nocapture %inArray, i32 %size) nounwind {
+entry:
+  %0 = icmp sgt i32 %size, 0
+  br i1 %0, label %loop, label %exit
+
+loop:                                          ; preds = %entry, %loop
+  %iv = phi i32 [ %iv1, %loop ], [ 0, %entry ]
+  %1 = getelementptr inbounds i32, i32* %inArray, i32 %iv
+  %2 = load i32, i32* %1, align 4
+  %3 = add nsw i32 %2, 6
+  store i32 %3, i32* %1, align 4
+  %iv1 = add i32 %iv, 1
+;  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %cond = icmp eq i32 %iv1, %size
+  br i1 %cond, label %exit, label %loop
+
+exit:                                         ; preds = %loop, %entry
+  ret void
+}
+
Index: lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
+++ lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
@@ -155,6 +155,10 @@
 }
 
 unsigned AMDGPUTTIImpl::getMaxInterleaveFactor(unsigned VF) {
+  // Disable unrolling if the loop is not vectorized.
+  if (VF == 1)
+    return 1;
+
   // Semi-arbitrary large amount.
   return 64;
 }


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