[PATCH] D82973: [InstCombine] Try to narrow expr if trunc cannot be removed.

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 275362.
fhahn marked an inline comment as done.
fhahn added a comment.

Use NewDestTy instead DestTy

In D82973#2125923 <https://reviews.llvm.org/D82973#2125923>, @spatel wrote:

> In D82973#2125918 <https://reviews.llvm.org/D82973#2125918>, @RKSimon wrote:
>
> > vector test cases? I realize for PR43580 we can get this done before vectorization
>
>
> We could add tests, but I don't think we can see changes as long as we are using shouldChangeType() to guard the transform:


Thanks, I added a vector test, but it won't be transformed currently, as I don't think there's an easy way to check if the new vector would be legal (as noted in shouldChangeType. Also, limiting to integer types allows using getExtendedType.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D82973/new/

https://reviews.llvm.org/D82973

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/trunc-binop-ext.ll


Index: llvm/test/Transforms/InstCombine/trunc-binop-ext.ll
===================================================================
--- llvm/test/Transforms/InstCombine/trunc-binop-ext.ll
+++ llvm/test/Transforms/InstCombine/trunc-binop-ext.ll
@@ -318,11 +318,11 @@
 ; Test cases for PR43580
 define i8 @narrow_zext_ashr_keep_trunc(i8 %i1, i8 %i2) {
 ; CHECK-LABEL: @narrow_zext_ashr_keep_trunc(
-; CHECK-NEXT:    [[I1_EXT:%.*]] = sext i8 [[I1:%.*]] to i32
-; CHECK-NEXT:    [[I2_EXT:%.*]] = sext i8 [[I2:%.*]] to i32
-; CHECK-NEXT:    [[SUB:%.*]] = add nsw i32 [[I1_EXT]], [[I2_EXT]]
-; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[SUB]], 1
-; CHECK-NEXT:    [[T:%.*]] = trunc i32 [[TMP1]] to i8
+; CHECK-NEXT:    [[I1_EXT:%.*]] = sext i8 [[I1:%.*]] to i16
+; CHECK-NEXT:    [[I2_EXT:%.*]] = sext i8 [[I2:%.*]] to i16
+; CHECK-NEXT:    [[SUB:%.*]] = add nsw i16 [[I1_EXT]], [[I2_EXT]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i16 [[SUB]], 1
+; CHECK-NEXT:    [[T:%.*]] = trunc i16 [[TMP1]] to i8
 ; CHECK-NEXT:    ret i8 [[T]]
 ;
   %i1.ext = sext i8 %i1 to i32
@@ -335,11 +335,11 @@
 
 define i8 @narrow_zext_ashr_keep_trunc2(i9 %i1, i9 %i2) {
 ; CHECK-LABEL: @narrow_zext_ashr_keep_trunc2(
-; CHECK-NEXT:    [[I1_EXT1:%.*]] = zext i9 [[I1:%.*]] to i64
-; CHECK-NEXT:    [[I2_EXT2:%.*]] = zext i9 [[I2:%.*]] to i64
-; CHECK-NEXT:    [[SUB:%.*]] = add nuw nsw i64 [[I1_EXT1]], [[I2_EXT2]]
-; CHECK-NEXT:    [[TMP1:%.*]] = lshr i64 [[SUB]], 1
-; CHECK-NEXT:    [[T:%.*]] = trunc i64 [[TMP1]] to i8
+; CHECK-NEXT:    [[I1_EXT1:%.*]] = zext i9 [[I1:%.*]] to i16
+; CHECK-NEXT:    [[I2_EXT2:%.*]] = zext i9 [[I2:%.*]] to i16
+; CHECK-NEXT:    [[SUB:%.*]] = add nuw nsw i16 [[I1_EXT1]], [[I2_EXT2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i16 [[SUB]], 1
+; CHECK-NEXT:    [[T:%.*]] = trunc i16 [[TMP1]] to i8
 ; CHECK-NEXT:    ret i8 [[T]]
 ;
   %i1.ext = sext i9 %i1 to i64
@@ -352,11 +352,11 @@
 
 define i7 @narrow_zext_ashr_keep_trunc3(i8 %i1, i8 %i2) {
 ; CHECK-LABEL: @narrow_zext_ashr_keep_trunc3(
-; CHECK-NEXT:    [[I1_EXT1:%.*]] = zext i8 [[I1:%.*]] to i64
-; CHECK-NEXT:    [[I2_EXT2:%.*]] = zext i8 [[I2:%.*]] to i64
-; CHECK-NEXT:    [[SUB:%.*]] = add nuw nsw i64 [[I1_EXT1]], [[I2_EXT2]]
-; CHECK-NEXT:    [[TMP1:%.*]] = lshr i64 [[SUB]], 1
-; CHECK-NEXT:    [[T:%.*]] = trunc i64 [[TMP1]] to i7
+; CHECK-NEXT:    [[I1_EXT1:%.*]] = zext i8 [[I1:%.*]] to i14
+; CHECK-NEXT:    [[I2_EXT2:%.*]] = zext i8 [[I2:%.*]] to i14
+; CHECK-NEXT:    [[SUB:%.*]] = add nuw nsw i14 [[I1_EXT1]], [[I2_EXT2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i14 [[SUB]], 1
+; CHECK-NEXT:    [[T:%.*]] = trunc i14 [[TMP1]] to i7
 ; CHECK-NEXT:    ret i7 [[T]]
 ;
   %i1.ext = sext i8 %i1 to i64
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -713,6 +713,25 @@
     return replaceInstUsesWith(Trunc, Res);
   }
 
+  // For integer types, check if we can shorten the entire input expression to
+  // DestWidth * 2, which won't allow removing the truncate, but reducing the
+  // width may enable further optimizations, e.g. allowing for larger
+  // vectorization factors.
+  if (auto *DestITy = dyn_cast<IntegerType>(DestTy)) {
+    if (DestWidth * 2 < SrcWidth) {
+      auto *NewDestTy = DestITy->getExtendedType();
+      if (shouldChangeType(SrcTy, DestTy) &&
+          canEvaluateTruncated(Src, NewDestTy, *this, &Trunc)) {
+        LLVM_DEBUG(
+            dbgs() << "ICE: EvaluateInDifferentType converting expression type"
+                      " to reduce the width of operand of"
+                   << Trunc << '\n');
+        Value *Res = EvaluateInDifferentType(Src, NewDestTy, false);
+        return new TruncInst(Res, DestTy);
+      }
+    }
+  }
+
   // Test if the trunc is the user of a select which is part of a
   // minimum or maximum operation. If so, don't do any more simplification.
   // Even simplifying demanded bits can break the canonical form of a


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