[llvm] 3b5f318 - [InstCombine] ror/rol(X, RotAmt) == C --> X == rol/ror(C, RotAmt) (PR51567)

[Dávid Bolvanský via llvm-commits]

Author: Dávid Bolvanský
Date: 2021-09-07T18:04:58+02:00
New Revision: 3b5f318f5d2df423afd3b5dddd824fc9a66db17b

URL: https://github.com/llvm/llvm-project/commit/3b5f318f5d2df423afd3b5dddd824fc9a66db17b
DIFF: https://github.com/llvm/llvm-project/commit/3b5f318f5d2df423afd3b5dddd824fc9a66db17b.diff

LOG: [InstCombine] ror/rol(X, RotAmt) == C --> X == rol/ror(C, RotAmt)   (PR51567)

```
----------------------------------------
define i1 @src(i32 %0) {
%1:
  %2 = fshl i32 %0, i32 %0, i32 25
  %3 = icmp eq i32 %2, 5
  ret i1 %3
}
=>
define i1 @tgt(i32 %0) {
%1:
  %2 = icmp eq i32 %0, 640
  ret i1 %2
}
Transformation seems to be correct!
```

https://alive2.llvm.org/ce/z/GdY8Jm

Solves PR51567

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D109283

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/icmp-rotate.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 4cc795647dbee..20411c9999273 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3228,12 +3228,22 @@ Instruction *InstCombinerImpl::foldICmpEqIntrinsicWithConstant(
 
   case Intrinsic::fshl:
   case Intrinsic::fshr:
-    // (rot X, ?) == 0/-1 --> X == 0/-1
-    // TODO: This transform is safe to re-use undef elts in a vector, but
-    //       the constant value passed in by the caller doesn't allow that.
-    if (C.isNullValue() || C.isAllOnesValue())
-      if (II->getArgOperand(0) == II->getArgOperand(1))
+    if (II->getArgOperand(0) == II->getArgOperand(1)) {
+      // (rot X, ?) == 0/-1 --> X == 0/-1
+      // TODO: This transform is safe to re-use undef elts in a vector, but
+      //       the constant value passed in by the caller doesn't allow that.
+      if (C.isNullValue() || C.isAllOnesValue())
         return new ICmpInst(Pred, II->getArgOperand(0), Cmp.getOperand(1));
+
+      const APInt *RotAmtC;
+      // ror(X, RotAmtC) == C --> X == rol(C, RotAmtC)
+      // rol(X, RotAmtC) == C --> X == ror(C, RotAmtC)
+      if (match(II->getArgOperand(2), m_APInt(RotAmtC)))
+        return new ICmpInst(Pred, II->getArgOperand(0),
+                            II->getIntrinsicID() == Intrinsic::fshl
+                                ? ConstantInt::get(Ty, C.rotr(*RotAmtC))
+                                : ConstantInt::get(Ty, C.rotl(*RotAmtC)));
+    }
     break;
 
   case Intrinsic::uadd_sat: {

diff  --git a/llvm/test/Transforms/InstCombine/icmp-rotate.ll b/llvm/test/Transforms/InstCombine/icmp-rotate.ll
index caf8cf8246d6f..5776c0e34dd11 100644
--- a/llvm/test/Transforms/InstCombine/icmp-rotate.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-rotate.ll
@@ -108,8 +108,7 @@ define <2 x i1> @ror_eq_vec(<2 x i5> %x, <2 x i5> %y, <2 x i5> %z) {
 
 define i1 @rol_eq_cst(i8 %x) {
 ; CHECK-LABEL: @rol_eq_cst(
-; CHECK-NEXT:    [[F:%.*]] = tail call i8 @llvm.fshl.i8(i8 [[X:%.*]], i8 [[X]], i8 3)
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[F]], 2
+; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[X:%.*]], 64
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %f = tail call i8 @llvm.fshl.i8(i8 %x, i8 %x, i8 3)
@@ -119,8 +118,7 @@ define i1 @rol_eq_cst(i8 %x) {
 
 define i1 @rol_ne_cst(i8 %x) {
 ; CHECK-LABEL: @rol_ne_cst(
-; CHECK-NEXT:    [[F:%.*]] = tail call i8 @llvm.fshl.i8(i8 [[X:%.*]], i8 [[X]], i8 3)
-; CHECK-NEXT:    [[R:%.*]] = icmp ne i8 [[F]], 2
+; CHECK-NEXT:    [[R:%.*]] = icmp ne i8 [[X:%.*]], 64
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %f = tail call i8 @llvm.fshl.i8(i8 %x, i8 %x, i8 3)
@@ -132,7 +130,7 @@ define i1 @rol_eq_cst_use(i8 %x) {
 ; CHECK-LABEL: @rol_eq_cst_use(
 ; CHECK-NEXT:    [[F:%.*]] = tail call i8 @llvm.fshl.i8(i8 [[X:%.*]], i8 [[X]], i8 3)
 ; CHECK-NEXT:    call void @use(i8 [[F]])
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[F]], 2
+; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[X]], 64
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %f = tail call i8 @llvm.fshl.i8(i8 %x, i8 %x, i8 3)
@@ -143,8 +141,7 @@ define i1 @rol_eq_cst_use(i8 %x) {
 
 define i1 @ror_eq_cst(i8 %x) {
 ; CHECK-LABEL: @ror_eq_cst(
-; CHECK-NEXT:    [[F:%.*]] = call i8 @llvm.fshl.i8(i8 [[X:%.*]], i8 [[X]], i8 6)
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[F]], 3
+; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[X:%.*]], 12
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %f = tail call i8 @llvm.fshr.i8(i8 %x, i8 %x, i8 2)
@@ -154,8 +151,7 @@ define i1 @ror_eq_cst(i8 %x) {
 
 define i1 @ror_ne_cst(i8 %x) {
 ; CHECK-LABEL: @ror_ne_cst(
-; CHECK-NEXT:    [[F:%.*]] = call i8 @llvm.fshl.i8(i8 [[X:%.*]], i8 [[X]], i8 6)
-; CHECK-NEXT:    [[R:%.*]] = icmp ne i8 [[F]], 3
+; CHECK-NEXT:    [[R:%.*]] = icmp ne i8 [[X:%.*]], 12
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %f = tail call i8 @llvm.fshr.i8(i8 %x, i8 %x, i8 2)
@@ -165,8 +161,7 @@ define i1 @ror_ne_cst(i8 %x) {
 
 define <2 x i1> @rol_eq_cst_vec(<2 x i5> %x) {
 ; CHECK-LABEL: @rol_eq_cst_vec(
-; CHECK-NEXT:    [[F:%.*]] = tail call <2 x i5> @llvm.fshl.v2i5(<2 x i5> [[X:%.*]], <2 x i5> [[X]], <2 x i5> <i5 3, i5 3>)
-; CHECK-NEXT:    [[R:%.*]] = icmp eq <2 x i5> [[F]], <i5 2, i5 2>
+; CHECK-NEXT:    [[R:%.*]] = icmp eq <2 x i5> [[X:%.*]], <i5 8, i5 8>
 ; CHECK-NEXT:    ret <2 x i1> [[R]]
 ;
   %f = tail call <2 x i5> @llvm.fshl.v2i5(<2 x i5> %x, <2 x i5> %x, <2 x i5> <i5 3, i5 3>)