[PATCH] D85043: [InstSimplify] simplify abs if operand is known non-negative

[Sanjay Patel via Phabricator via llvm-commits]

spatel updated this revision to Diff 282340.
spatel added a comment.

Patch updated:
Pass in more info from the SimplifyQuery to ValueTracking. 
Not sure what it takes to show the benefit, so no test diffs, but if there are suggestions, let me know.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85043/new/

https://reviews.llvm.org/D85043

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/call.ll


Index: llvm/test/Transforms/InstSimplify/call.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/call.ll
+++ llvm/test/Transforms/InstSimplify/call.ll
@@ -5,13 +5,12 @@
 declare i32 @llvm.abs.i32(i32, i1)
 declare <3 x i82> @llvm.abs.v3i82(<3 x i82>, i1)
 
-; TODO: If the sign bit is known zero, the abs is not needed.
+; If the sign bit is known zero, the abs is not needed.
 
 define i32 @zext_abs(i31 %x) {
 ; CHECK-LABEL: @zext_abs(
 ; CHECK-NEXT:    [[ZEXT:%.*]] = zext i31 [[X:%.*]] to i32
-; CHECK-NEXT:    [[ABS:%.*]] = call i32 @llvm.abs.i32(i32 [[ZEXT]], i1 false)
-; CHECK-NEXT:    ret i32 [[ABS]]
+; CHECK-NEXT:    ret i32 [[ZEXT]]
 ;
   %zext = zext i31 %x to i32
   %abs = call i32 @llvm.abs.i32(i32 %zext, i1 false)
@@ -21,8 +20,7 @@
 define <3 x i82> @lshr_abs(<3 x i82> %x) {
 ; CHECK-LABEL: @lshr_abs(
 ; CHECK-NEXT:    [[LSHR:%.*]] = lshr <3 x i82> [[X:%.*]], <i82 1, i82 1, i82 1>
-; CHECK-NEXT:    [[ABS:%.*]] = call <3 x i82> @llvm.abs.v3i82(<3 x i82> [[LSHR]], i1 true)
-; CHECK-NEXT:    ret <3 x i82> [[ABS]]
+; CHECK-NEXT:    ret <3 x i82> [[LSHR]]
 ;
   %lshr = lshr <3 x i82> %x, <i82 1, i82 1, i82 1>
   %abs = call <3 x i82> @llvm.abs.v3i82(<3 x i82> %lshr, i1 true)
@@ -32,8 +30,7 @@
 define i32 @and_abs(i32 %x) {
 ; CHECK-LABEL: @and_abs(
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[X:%.*]], 2147483644
-; CHECK-NEXT:    [[ABS:%.*]] = call i32 @llvm.abs.i32(i32 [[AND]], i1 true)
-; CHECK-NEXT:    ret i32 [[ABS]]
+; CHECK-NEXT:    ret i32 [[AND]]
 ;
   %and = and i32 %x, 2147483644
   %abs = call i32 @llvm.abs.i32(i32 %and, i1 true)
@@ -43,8 +40,7 @@
 define <3 x i82> @select_abs(<3 x i1> %cond) {
 ; CHECK-LABEL: @select_abs(
 ; CHECK-NEXT:    [[SEL:%.*]] = select <3 x i1> [[COND:%.*]], <3 x i82> zeroinitializer, <3 x i82> <i82 2147483647, i82 42, i82 1>
-; CHECK-NEXT:    [[ABS:%.*]] = call <3 x i82> @llvm.abs.v3i82(<3 x i82> [[SEL]], i1 false)
-; CHECK-NEXT:    ret <3 x i82> [[ABS]]
+; CHECK-NEXT:    ret <3 x i82> [[SEL]]
 ;
   %sel = select <3 x i1> %cond, <3 x i82> zeroinitializer, <3 x i82> <i82 2147483647, i82 42, i82 1>
   %abs = call <3 x i82> @llvm.abs.v3i82(<3 x i82> %sel, i1 false)
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5255,6 +5255,12 @@
   Type *ReturnType = F->getReturnType();
   unsigned BitWidth = ReturnType->getScalarSizeInBits();
   switch (IID) {
+  case Intrinsic::abs:
+    // If the sign bit is clear already, then abs does not do anything.
+    if (isKnownNonNegative(Op0, Q.DL, 0, Q.AC, Q.CxtI, Q.DT))
+      return Op0;
+    break;
+
   case Intrinsic::smax:
   case Intrinsic::smin:
   case Intrinsic::umax:


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