[llvm] c982682 - [EarlyCSE] Equivalent SELECTs should hash equally

[Bryan Chan via llvm-commits]

Author: Bryan Chan
Date: 2020-09-10T16:59:24-04:00
New Revision: c9826829d74e637163fdb0351870b8204e62d6e6

URL: https://github.com/llvm/llvm-project/commit/c9826829d74e637163fdb0351870b8204e62d6e6
DIFF: https://github.com/llvm/llvm-project/commit/c9826829d74e637163fdb0351870b8204e62d6e6.diff

LOG: [EarlyCSE] Equivalent SELECTs should hash equally

DenseMap<SimpleValue> assumes that, if its isEqual method returns true
for two elements, then its getHashValue method must return the same value
for them. This invariant is broken when one SELECT node is a min/max
operation, and the other can be transformed into an equivalent min/max by
inverting its predicate and swapping its operands. This patch fixes an
assertion failure that would occur intermittently while compiling the
following IR:

    define i32 @t(i32 %i) {
      %cmp = icmp sle i32 0, %i
      %twin1 = select i1 %cmp, i32 %i, i32 0
      %cmpinv = icmp sgt i32 0, %i
      %twin2 = select i1 %cmpinv,  i32 0, i32 %i
      %sink = add i32 %twin1, %twin2
      ret i32 %sink
    }

Differential Revision: https://reviews.llvm.org/D86843

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/EarlyCSE.cpp
    llvm/test/Transforms/EarlyCSE/commute.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index b655204d26dd..f0d3f90995d7 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -191,6 +191,19 @@ static bool matchSelectWithOptionalNotCond(Value *V, Value *&Cond, Value *&A,
     Pred = ICmpInst::getSwappedPredicate(Pred);
   }
 
+  // Check for inverted variants of min/max by swapping operands.
+  switch (Pred) {
+  case CmpInst::ICMP_ULE:
+  case CmpInst::ICMP_UGE:
+  case CmpInst::ICMP_SLE:
+  case CmpInst::ICMP_SGE:
+    Pred = CmpInst::getInversePredicate(Pred);
+    std::swap(A, B);
+    break;
+  default:
+    break;
+  }
+
   switch (Pred) {
   case CmpInst::ICMP_UGT: Flavor = SPF_UMAX; break;
   case CmpInst::ICMP_ULT: Flavor = SPF_UMIN; break;

diff  --git a/llvm/test/Transforms/EarlyCSE/commute.ll b/llvm/test/Transforms/EarlyCSE/commute.ll
index 57c5a853a12f..f5868a5fdfb2 100644
--- a/llvm/test/Transforms/EarlyCSE/commute.ll
+++ b/llvm/test/Transforms/EarlyCSE/commute.ll
@@ -684,6 +684,25 @@ define i32 @select_not_invert_pred_cond_wrong_select_op(i8 %x, i8 %y, i32 %t, i3
   ret i32 %r
 }
 
+; This test is a reproducer for a bug involving inverted min/max selects
+; hashing 
diff erently but comparing as equal.  It exhibits such a pair of
+; values, and we run this test with -earlycse-debug-hash which would catch
+; the disagreement and fail if it regressed.
+define i32 @inverted_max(i32 %i) {
+; CHECK-LABEL: @inverted_max(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sle i32 0, [[I:%.*]]
+; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP]], i32 [[I]], i32 0
+; CHECK-NEXT:    [[CMPINV:%.*]] = icmp sgt i32 0, [[I:%.*]]
+; CHECK-NEXT:    [[M2:%.*]] = select i1 [[CMPINV]], i32 0, i32 [[I]]
+; CHECK-NEXT:    [[R:%.*]] = add i32 [[M1]], [[M2]]
+; CHECK-NEXT:    ret i32 [[R]]
+  %cmp = icmp sle i32 0, %i
+  %m1 = select i1 %cmp, i32 %i, i32 0
+  %cmpinv = icmp sgt i32 0, %i
+  %m2 = select i1 %cmpinv, i32 0, i32 %i
+  %r = add i32 %m1, %m2
+  ret i32 %r
+}
 
 ; This test is a reproducer for a bug involving inverted min/max selects
 ; hashing 
diff erently but comparing as equal.  It exhibits such a pair of