[llvm] 467cbb6 - [InstCombine] fold more constant divisor to select-of-constants divisor

[Chenbing Zheng via llvm-commits]

Author: Chenbing Zheng
Date: 2022-04-08T10:19:24+08:00
New Revision: 467cbb6249df671bccb5837c4e8f36a0646e29ae

URL: https://github.com/llvm/llvm-project/commit/467cbb6249df671bccb5837c4e8f36a0646e29ae
DIFF: https://github.com/llvm/llvm-project/commit/467cbb6249df671bccb5837c4e8f36a0646e29ae.diff

LOG: [InstCombine] fold more constant divisor to select-of-constants divisor

By adding a parameter to function FoldOpIntoSelect， we can fold more Ops to Select.
For this example, we tend to fold the division instruction,
so we no longer care whether SelectInst is one use.

This patch slove TODO left in InstCombine/div.ll.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D122967

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineInternal.h
    llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/test/Transforms/InstCombine/div.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 6bcae604dcf91..fd4faca46e3b2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -622,7 +622,8 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
   /// other operand, try to fold the binary operator into the select arguments.
   /// This also works for Cast instructions, which obviously do not have a
   /// second operand.
-  Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI);
+  Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI,
+                                bool FoldWithMultiUse = false);
 
   /// This is a convenience wrapper function for the above two functions.
   Instruction *foldBinOpIntoSelectOrPhi(BinaryOperator &I);

diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index a1eeb67a0ec0b..41717577c2266 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -772,7 +772,8 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
   // TODO: Adapt simplifyDivRemOfSelectWithZeroOp to allow this and other folds.
   if (match(Op0, m_ImmConstant()) &&
       match(Op1, m_Select(m_Value(), m_ImmConstant(), m_ImmConstant()))) {
-    if (Instruction *R = FoldOpIntoSelect(I, cast<SelectInst>(Op1)))
+    if (Instruction *R = FoldOpIntoSelect(I, cast<SelectInst>(Op1),
+                                          /*FoldWithMultiUse*/ true))
       return R;
   }
 

diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index c8368d559e253..51ef4b11ddc8e 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1037,10 +1037,10 @@ static Value *foldOperationIntoSelectOperand(Instruction &I, Value *SO,
   return NewBO;
 }
 
-Instruction *InstCombinerImpl::FoldOpIntoSelect(Instruction &Op,
-                                                SelectInst *SI) {
-  // Don't modify shared select instructions.
-  if (!SI->hasOneUse())
+Instruction *InstCombinerImpl::FoldOpIntoSelect(Instruction &Op, SelectInst *SI,
+                                                bool FoldWithMultiUse) {
+  // Don't modify shared select instructions unless set FoldWithMultiUse
+  if (!SI->hasOneUse() && !FoldWithMultiUse)
     return nullptr;
 
   Value *TV = SI->getTrueValue();

diff  --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index 14e76e6ee6398..165caaaa652be 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -1098,13 +1098,11 @@ define i32 @sdiv_constant_dividend_select_of_constants_divisor(i1 %b) {
   ret i32 %r
 }
 
-; TODO: sdiv should still be replaced by select.
-
 define i32 @sdiv_constant_dividend_select_of_constants_divisor_use(i1 %b) {
 ; CHECK-LABEL: @sdiv_constant_dividend_select_of_constants_divisor_use(
 ; CHECK-NEXT:    [[S:%.*]] = select i1 [[B:%.*]], i32 12, i32 -3
 ; CHECK-NEXT:    call void @use(i32 [[S]])
-; CHECK-NEXT:    [[R:%.*]] = sdiv i32 42, [[S]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i32 3, i32 -14
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %s = select i1 %b, i32 12, i32 -3
@@ -1204,13 +1202,11 @@ define i32 @udiv_constant_dividend_select_of_constants_divisor(i1 %b) {
   ret i32 %r
 }
 
-; TODO: udiv should still be replaced by select.
-
 define i32 @udiv_constant_dividend_select_of_constants_divisor_use(i1 %b) {
 ; CHECK-LABEL: @udiv_constant_dividend_select_of_constants_divisor_use(
 ; CHECK-NEXT:    [[S:%.*]] = select i1 [[B:%.*]], i32 12, i32 -3
 ; CHECK-NEXT:    call void @use(i32 [[S]])
-; CHECK-NEXT:    [[R:%.*]] = udiv i32 42, [[S]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i32 3, i32 0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %s = select i1 %b, i32 12, i32 -3