[llvm] r264852 - [VectorUtils] Don't try and truncate PHIs to a smaller bitwidth

[James Molloy via llvm-commits]

Author: jamesm
Date: Wed Mar 30 05:11:43 2016
New Revision: 264852

URL: http://llvm.org/viewvc/llvm-project?rev=264852&view=rev
Log:
[VectorUtils] Don't try and truncate PHIs to a smaller bitwidth

We already try not to truncate PHIs in computeMinimalBitwidths. LoopVectorize can't handle it and we really don't need to, because both induction and reduction PHIs are truncated by other means.

However, we weren't bailing out in all the places we should have, and we ended up by returning a PHI to be truncated, which has caused PR27018.

This fixes PR17018.

Modified:
    llvm/trunk/lib/Analysis/VectorUtils.cpp
    llvm/trunk/test/Transforms/LoopVectorize/AArch64/loop-vectorization-factors.ll

Modified: llvm/trunk/lib/Analysis/VectorUtils.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/VectorUtils.cpp?rev=264852&r1=264851&r2=264852&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/VectorUtils.cpp (original)
+++ llvm/trunk/lib/Analysis/VectorUtils.cpp Wed Mar 30 05:11:43 2016
@@ -499,6 +499,7 @@ llvm::computeMinimumValueSizes(ArrayRef<
 
     uint64_t V = DB.getDemandedBits(I).getZExtValue();
     DBits[Leader] |= V;
+    DBits[I] = V;
 
     // Casts, loads and instructions outside of our range terminate a chain
     // successfully.
@@ -549,6 +550,20 @@ llvm::computeMinimumValueSizes(ArrayRef<
     // Round up to a power of 2
     if (!isPowerOf2_64((uint64_t)MinBW))
       MinBW = NextPowerOf2(MinBW);
+
+    // We don't modify the types of PHIs. Reductions will already have been
+    // truncated if possible, and inductions' sizes will have been chosen by
+    // indvars.
+    // If we are required to shrink a PHI, abandon this entire equivalence class.
+    bool Abort = false;
+    for (auto MI = ECs.member_begin(I), ME = ECs.member_end(); MI != ME; ++MI)
+      if (isa<PHINode>(*MI) && MinBW < (*MI)->getType()->getScalarSizeInBits()) {
+        Abort = true;
+        break;
+      }
+    if (Abort)
+      continue;
+
     for (auto MI = ECs.member_begin(I), ME = ECs.member_end(); MI != ME; ++MI) {
       if (!isa<Instruction>(*MI))
         continue;

Modified: llvm/trunk/test/Transforms/LoopVectorize/AArch64/loop-vectorization-factors.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/AArch64/loop-vectorization-factors.ll?rev=264852&r1=264851&r2=264852&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/AArch64/loop-vectorization-factors.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/AArch64/loop-vectorization-factors.ll Wed Mar 30 05:11:43 2016
@@ -205,5 +205,63 @@ for.body:
   br i1 %exitcond, label %for.cond.cleanup, label %for.body
 }
 
+; CHECK-LABEL: @add_phifail(
+; CHECK: load <16 x i8>, <16 x i8>*
+; CHECK: add nuw nsw <16 x i32>
+; CHECK: store <16 x i8>
+; Function Attrs: nounwind
+define void @add_phifail(i8* noalias nocapture readonly %p, i8* noalias nocapture %q, i32 %len) #0 {
+entry:
+  %cmp8 = icmp sgt i32 %len, 0
+  br i1 %cmp8, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup:                                 ; preds = %for.body, %entry
+  ret void
+
+for.body:                                         ; preds = %entry, %for.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
+  %a_phi = phi i32 [ %conv, %for.body ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i8, i8* %p, i64 %indvars.iv
+  %0 = load i8, i8* %arrayidx
+  %conv = zext i8 %0 to i32
+  %add = add nuw nsw i32 %conv, 2
+  %conv1 = trunc i32 %add to i8
+  %arrayidx3 = getelementptr inbounds i8, i8* %q, i64 %indvars.iv
+  store i8 %conv1, i8* %arrayidx3
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %len
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+; CHECK-LABEL: @add_phifail2(
+; CHECK: load <16 x i8>, <16 x i8>*
+; CHECK: add nuw nsw <16 x i32>
+; CHECK: store <16 x i8>
+; Function Attrs: nounwind
+define i8 @add_phifail2(i8* noalias nocapture readonly %p, i8* noalias nocapture %q, i32 %len) #0 {
+entry:
+  br label %for.body
+
+for.cond.cleanup:                                 ; preds = %for.body, %entry
+  %ret = trunc i32 %a_phi to i8
+  ret i8 %ret
+
+for.body:                                         ; preds = %entry, %for.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
+  %a_phi = phi i32 [ %conv, %for.body ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i8, i8* %p, i64 %indvars.iv
+  %0 = load i8, i8* %arrayidx
+  %conv = zext i8 %0 to i32
+  %add = add nuw nsw i32 %conv, 2
+  %conv1 = trunc i32 %add to i8
+  %arrayidx3 = getelementptr inbounds i8, i8* %q, i64 %indvars.iv
+  store i8 %conv1, i8* %arrayidx3
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %len
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
 
 attributes #0 = { nounwind }
+