From 08c08577f94fd7efd2a670d0e5c3c6f72882fa0a Mon Sep 17 00:00:00 2001
From: =?utf8?q?D=C3=A1vid=20Bolvansk=C3=BD?= <david.bolvansky@gmail.com>
Date: Mon, 3 May 2021 23:59:19 +0200
Subject: [PATCH] [InstCombine] cttz(sext(x)) -> cttz(zext(x))

```

----------------------------------------
define i32 @src(i16 %x, i1 %b) {
%0:
  %z = sext i16 %x to i32
  %p = cttz i32 %z, %b
  ret i32 %p
}
=>
define i32 @tgt(i16 %x, i1 %b) {
%0:
  %z = zext i16 %x to i32
  %p = cttz i32 %z, %b
  ret i32 %p
}
Transformation seems to be correct!
```

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

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D101764
---
 .../Transforms/InstCombine/InstCombineCalls.cpp    |  8 +++++++
 llvm/test/Transforms/InstCombine/cttz.ll           | 26 +++++++++++-----------
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 15740bb..b2e173de 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -439,6 +439,14 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
     if (match(Op0, m_Neg(m_Value(X))))
       return IC.replaceOperand(II, 0, X);
 
+    // cttz(sext(x)) -> cttz(zext(x))
+    if (match(Op0, m_OneUse(m_SExt(m_Value(X))))) {
+      auto *Zext = IC.Builder.CreateZExt(X, II.getType());
+      auto *CttzZext =
+          IC.Builder.CreateBinaryIntrinsic(Intrinsic::cttz, Zext, Op1);
+      return IC.replaceInstUsesWith(II, CttzZext);
+    }
+
     // Zext doesn't change the number of trailing zeros, so narrow:
     // cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true'.
     if (match(Op0, m_OneUse(m_ZExt(m_Value(X)))) && match(Op1, m_One())) {
diff --git a/llvm/test/Transforms/InstCombine/cttz.ll b/llvm/test/Transforms/InstCombine/cttz.ll
index 8d50c68..dd027de 100644
--- a/llvm/test/Transforms/InstCombine/cttz.ll
+++ b/llvm/test/Transforms/InstCombine/cttz.ll
@@ -64,9 +64,9 @@ define <2 x i64> @cttz_zext_zero_def_vec(<2 x i32> %x) {
 
 define i32 @cttz_sext_zero_undef(i16 %x) {
 ; CHECK-LABEL: @cttz_sext_zero_undef(
-; CHECK-NEXT:    [[S:%.*]] = sext i16 [[X:%.*]] to i32
-; CHECK-NEXT:    [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 true), !range [[RNG1]]
-; CHECK-NEXT:    ret i32 [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i16 @llvm.cttz.i16(i16 [[X:%.*]], i1 true), !range [[RNG0]]
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i16 [[TMP1]] to i32
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %s = sext i16 %x to i32
   %tz = call i32 @llvm.cttz.i32(i32 %s, i1 true)
@@ -75,11 +75,11 @@ define i32 @cttz_sext_zero_undef(i16 %x) {
 
 define i32 @cttz_sext_zero_def(i16 %x) {
 ; CHECK-LABEL: @cttz_sext_zero_def(
-; CHECK-NEXT:    [[S:%.*]] = zext i16 [[X:%.*]] to i32
-; CHECK-NEXT:    [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 false), !range [[RNG1]]
-; CHECK-NEXT:    ret i32 [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    [[TMP2:%.*]] = call i32 @llvm.cttz.i32(i32 [[TMP1]], i1 false), !range [[RNG1]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
-  %s = zext i16 %x to i32
+  %s = sext i16 %x to i32
   %tz = call i32 @llvm.cttz.i32(i32 %s, i1 false)
   ret i32 %tz
 }
@@ -99,9 +99,9 @@ define i32 @cttz_sext_zero_undef_extra_use(i16 %x) {
 
 define <2 x i64> @cttz_sext_zero_undef_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @cttz_sext_zero_undef_vec(
-; CHECK-NEXT:    [[S:%.*]] = sext <2 x i32> [[X:%.*]] to <2 x i64>
-; CHECK-NEXT:    [[TZ:%.*]] = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[S]], i1 true)
-; CHECK-NEXT:    ret <2 x i64> [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[X:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP2:%.*]] = zext <2 x i32> [[TMP1]] to <2 x i64>
+; CHECK-NEXT:    ret <2 x i64> [[TMP2]]
 ;
   %s = sext <2 x i32> %x to <2 x i64>
   %tz = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> %s, i1 true)
@@ -110,9 +110,9 @@ define <2 x i64> @cttz_sext_zero_undef_vec(<2 x i32> %x) {
 
 define <2 x i64> @cttz_sext_zero_def_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @cttz_sext_zero_def_vec(
-; CHECK-NEXT:    [[S:%.*]] = sext <2 x i32> [[X:%.*]] to <2 x i64>
-; CHECK-NEXT:    [[TZ:%.*]] = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[S]], i1 false)
-; CHECK-NEXT:    ret <2 x i64> [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext <2 x i32> [[X:%.*]] to <2 x i64>
+; CHECK-NEXT:    [[TMP2:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[TMP1]], i1 false)
+; CHECK-NEXT:    ret <2 x i64> [[TMP2]]
 ;
   %s = sext <2 x i32> %x to <2 x i64>
   %tz = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> %s, i1 false)
-- 
2.7.4