[PATCH] D87161: [DemandedBits][BDCE] Add support for min/max intrinsics

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
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Add DemandedBits / BDCE support for min/max intrinsics: If the low bits are not demanded in the result, they also aren't demanded in the operands.

We'll want the same in InstCombineSimplifyDemanded, but we need KnownBits support to land first, so that's waiting on D87034 <https://reviews.llvm.org/D87034>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D87161

Files:
  llvm/lib/Analysis/DemandedBits.cpp
  llvm/test/Transforms/BDCE/intrinsics.ll


Index: llvm/test/Transforms/BDCE/intrinsics.ll
===================================================================
--- llvm/test/Transforms/BDCE/intrinsics.ll
+++ llvm/test/Transforms/BDCE/intrinsics.ll
@@ -8,8 +8,8 @@
 
 define i8 @umax(i8 %x, i8 %y, i1 %a, i1 %b) {
 ; CHECK-LABEL: @umax(
-; CHECK-NEXT:    [[A2:%.*]] = zext i1 [[A:%.*]] to i8
-; CHECK-NEXT:    [[B2:%.*]] = zext i1 [[B:%.*]] to i8
+; CHECK-NEXT:    [[A2:%.*]] = zext i1 false to i8
+; CHECK-NEXT:    [[B2:%.*]] = zext i1 false to i8
 ; CHECK-NEXT:    [[X2:%.*]] = or i8 [[X:%.*]], [[A2]]
 ; CHECK-NEXT:    [[Y2:%.*]] = or i8 [[Y:%.*]], [[B2]]
 ; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.umax.i8(i8 [[X2]], i8 [[Y2]])
@@ -27,8 +27,8 @@
 
 define i8 @umin(i8 %x, i8 %y, i1 %a, i1 %b) {
 ; CHECK-LABEL: @umin(
-; CHECK-NEXT:    [[A2:%.*]] = zext i1 [[A:%.*]] to i8
-; CHECK-NEXT:    [[B2:%.*]] = zext i1 [[B:%.*]] to i8
+; CHECK-NEXT:    [[A2:%.*]] = zext i1 false to i8
+; CHECK-NEXT:    [[B2:%.*]] = zext i1 false to i8
 ; CHECK-NEXT:    [[X2:%.*]] = or i8 [[X:%.*]], [[A2]]
 ; CHECK-NEXT:    [[Y2:%.*]] = or i8 [[Y:%.*]], [[B2]]
 ; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.umin.i8(i8 [[X2]], i8 [[Y2]])
@@ -46,8 +46,8 @@
 
 define i8 @smax(i8 %x, i8 %y, i1 %a, i1 %b) {
 ; CHECK-LABEL: @smax(
-; CHECK-NEXT:    [[A2:%.*]] = zext i1 [[A:%.*]] to i8
-; CHECK-NEXT:    [[B2:%.*]] = zext i1 [[B:%.*]] to i8
+; CHECK-NEXT:    [[A2:%.*]] = zext i1 false to i8
+; CHECK-NEXT:    [[B2:%.*]] = zext i1 false to i8
 ; CHECK-NEXT:    [[X2:%.*]] = or i8 [[X:%.*]], [[A2]]
 ; CHECK-NEXT:    [[Y2:%.*]] = or i8 [[Y:%.*]], [[B2]]
 ; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.smax.i8(i8 [[X2]], i8 [[Y2]])
@@ -65,8 +65,8 @@
 
 define i8 @smin(i8 %x, i8 %y, i1 %a, i1 %b) {
 ; CHECK-LABEL: @smin(
-; CHECK-NEXT:    [[A2:%.*]] = zext i1 [[A:%.*]] to i8
-; CHECK-NEXT:    [[B2:%.*]] = zext i1 [[B:%.*]] to i8
+; CHECK-NEXT:    [[A2:%.*]] = zext i1 false to i8
+; CHECK-NEXT:    [[B2:%.*]] = zext i1 false to i8
 ; CHECK-NEXT:    [[X2:%.*]] = or i8 [[X:%.*]], [[A2]]
 ; CHECK-NEXT:    [[Y2:%.*]] = or i8 [[Y:%.*]], [[B2]]
 ; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.smin.i8(i8 [[X2]], i8 [[Y2]])
Index: llvm/lib/Analysis/DemandedBits.cpp
===================================================================
--- llvm/lib/Analysis/DemandedBits.cpp
+++ llvm/lib/Analysis/DemandedBits.cpp
@@ -170,6 +170,14 @@
         }
         break;
       }
+      case Intrinsic::umax:
+      case Intrinsic::umin:
+      case Intrinsic::smax:
+      case Intrinsic::smin:
+        // If low bits of result are not demanded, they are also not demanded
+        // for the min/max operands.
+        AB = APInt::getBitsSetFrom(BitWidth, AOut.countTrailingZeros());
+        break;
       }
     break;
   case Instruction::Add:


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