[PATCH] D104038: [InstCombine] Check if zext src and trunc dst have same types

[Datta Nagraj via Phabricator via llvm-commits]

datta.nagraj created this revision.
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Apply the opt only if zext src and trunc dst have same type and
do it only for datatypes of width more than 5, as for width less
than 6, this opt fails:

https://alive2.llvm.org/ce/z/5ThC64

The opt to be applied when width is less than 6 is shown here:

https://alive2.llvm.org/ce/z/ZtZm4w


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D104038

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/zext-ctlz-trunc-to-ctlz-add.ll


Index: llvm/test/Transforms/InstCombine/zext-ctlz-trunc-to-ctlz-add.ll
===================================================================
--- llvm/test/Transforms/InstCombine/zext-ctlz-trunc-to-ctlz-add.ll
+++ llvm/test/Transforms/InstCombine/zext-ctlz-trunc-to-ctlz-add.ll
@@ -71,8 +71,8 @@
 define <vscale x 2 x i16> @trunc_ctlz_zext_nxv2i16_nxv2i63_multiple_uses(<vscale x 2 x i16> %x) {
 ; CHECK-LABEL: @trunc_ctlz_zext_nxv2i16_nxv2i63_multiple_uses(
 ; CHECK-NEXT:    [[Z:%.*]] = zext <vscale x 2 x i16> [[X:%.*]] to <vscale x 2 x i63>
-; CHECK-NEXT:    [[P:%.*]] = call <vscale x 2 x i63> @llvm.ctlz.nxv2i63(<vscale x 2 x i63> [[Z]], i1 true)
-; CHECK-NEXT:    [[ZZ:%.*]] = trunc <vscale x 2 x i63> [[P]] to <vscale x 2 x i16>
+; CHECK-NEXT:    [[TMP1:%.*]] = call <vscale x 2 x i16> @llvm.ctlz.nxv2i16(<vscale x 2 x i16> [[X]], i1 true)
+; CHECK-NEXT:    [[ZZ:%.*]] = add nuw nsw <vscale x 2 x i16> [[TMP1]], shufflevector (<vscale x 2 x i16> insertelement (<vscale x 2 x i16> undef, i16 47, i32 0), <vscale x 2 x i16> undef, <vscale x 2 x i32> zeroinitializer)
 ; CHECK-NEXT:    call void @use1(<vscale x 2 x i63> [[Z]])
 ; CHECK-NEXT:    ret <vscale x 2 x i16> [[ZZ]]
 ;
@@ -83,3 +83,33 @@
   ret <vscale x 2 x i16> %zz
 }
 
+; Negative case where types of x and zz don't match
+
+define i16 @trunc_ctlz_zext_i10_i32(i10 %x) {
+; CHECK-LABEL: @trunc_ctlz_zext_i10_i32(
+; CHECK-NEXT:    [[Z:%.*]] = zext i10 [[X:%.*]] to i32
+; CHECK-NEXT:    [[P:%.*]] = call i32 @llvm.ctlz.i32(i32 [[Z]], i1 false), !range [[RNG1:![0-9]+]]
+; CHECK-NEXT:    [[ZZ:%.*]] = trunc i32 [[P]] to i16
+; CHECK-NEXT:    ret i16 [[ZZ]]
+;
+  %z = zext i10 %x to i32
+  %p = call i32 @llvm.ctlz.i32(i32 %z, i1 false)
+  %zz = trunc i32 %p to i16
+  ret i16 %zz
+}
+
+; Negative case where size of x is less than 6
+
+define i5 @trunc_ctlz_zext_i5_i32(i5 %x) {
+; CHECK-LABEL: @trunc_ctlz_zext_i5_i32(
+; CHECK-NEXT:    [[Z:%.*]] = zext i5 [[X:%.*]] to i32
+; CHECK-NEXT:    [[P:%.*]] = call i32 @llvm.ctlz.i32(i32 [[Z]], i1 false), !range [[RNG2:![0-9]+]]
+; CHECK-NEXT:    [[ZZ:%.*]] = trunc i32 [[P]] to i5
+; CHECK-NEXT:    ret i5 [[ZZ]]
+;
+  %z = zext i5 %x to i32
+  %p = call i32 @llvm.ctlz.i32(i32 %z, i1 false)
+  %zz = trunc i32 %p to i5
+  ret i5 %zz
+}
+
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -951,15 +951,16 @@
   }
 
   // trunc (ctlz_i32(zext(A), B) --> add(ctlz_i16(A, B), C)
-  if (match(Src, m_OneUse(m_Intrinsic<Intrinsic::ctlz>(
-                     m_OneUse(m_ZExt(m_Value(A))), m_Value(B))))) {
-    Value *WidthDiff =
-        ConstantInt::get(A->getType(), Src->getType()->getScalarSizeInBits() -
-                                           A->getType()->getScalarSizeInBits());
-
-    Value *NarrowCtlz =
-        Builder.CreateIntrinsic(Intrinsic::ctlz, {Trunc.getType()}, {A, B});
-    return BinaryOperator::CreateAdd(NarrowCtlz, WidthDiff);
+  if (match(Src, m_OneUse(m_Intrinsic<Intrinsic::ctlz>(m_ZExt(m_Value(A)),
+                                                       m_Value(B))))) {
+    unsigned AWidth = A->getType()->getScalarSizeInBits();
+
+    if (AWidth == DestWidth && AWidth > 5) {
+      Value *WidthDiff = ConstantInt::get(A->getType(), SrcWidth - AWidth);
+      Value *NarrowCtlz =
+          Builder.CreateIntrinsic(Intrinsic::ctlz, {Trunc.getType()}, {A, B});
+      return BinaryOperator::CreateAdd(NarrowCtlz, WidthDiff);
+    }
   }
   return nullptr;
 }


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