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

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: craig.topper, nikic, lebedev.ri, RKSimon.
Herald added subscribers: steven.zhang, hiraditya, mcrosier.
Herald added a project: LLVM.
spatel requested review of this revision.

abs() should be rare enough that using value tracking is not going to be a compile-time cost burden, so use it to reduce a variety of potential patterns. We do this in DAGCombiner too.


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))
+      return Op0;
+    break;
+
   case Intrinsic::smax:
   case Intrinsic::smin:
   case Intrinsic::umax:


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D85043.282308.patch
Type: text/x-patch
Size: 2790 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200731/4e4c7ce5/attachment.bin>