[PATCH] D101807: [InstCombine] Fold select x_inv, true, (select y, x, false)

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune created this revision.
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This is a simple folding that optimizes

  select x_inv, true, (select y, x, false)

to

  select x_inv, true, y


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101807

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/select-safe-transforms.ll


Index: llvm/test/Transforms/InstCombine/select-safe-transforms.ll
===================================================================
--- llvm/test/Transforms/InstCombine/select-safe-transforms.ll
+++ llvm/test/Transforms/InstCombine/select-safe-transforms.ll
@@ -181,10 +181,8 @@
 
 define i1 @orn_and_cmp_1_logical(i37 %a, i37 %b, i1 %y) {
 ; CHECK-LABEL: @orn_and_cmp_1_logical(
-; CHECK-NEXT:    [[X:%.*]] = icmp sgt i37 [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT:    [[X_INV:%.*]] = icmp sle i37 [[A]], [[B]]
-; CHECK-NEXT:    [[AND:%.*]] = select i1 [[Y:%.*]], i1 [[X]], i1 false
-; CHECK-NEXT:    [[OR:%.*]] = select i1 [[X_INV]], i1 true, i1 [[AND]]
+; CHECK-NEXT:    [[X_INV:%.*]] = icmp sle i37 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[OR:%.*]] = select i1 [[X_INV]], i1 true, i1 [[Y:%.*]]
 ; CHECK-NEXT:    ret i1 [[OR]]
 ;
   %x = icmp sgt i37 %a, %b
Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2773,6 +2773,14 @@
       if (Res && *Res == false)
         return replaceOperand(SI, 1, A);
     }
+    // select c, true, (select a, b, false)  -> select c, true, a
+    //   if c = false implies that b = true
+    if (match(TrueVal, m_One()) &&
+        match(FalseVal, m_Select(m_Value(A), m_Value(B), m_Zero()))) {
+      Optional<bool> Res = isImpliedCondition(CondVal, B, DL, false);
+      if (Res && *Res == true)
+        return replaceOperand(SI, 2, A);
+    }
 
     // sel (sel c, a, false), true, (sel !c, b, false) -> sel c, a, b
     // sel (sel !c, a, false), true, (sel c, b, false) -> sel c, b, a


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