[llvm] 457bd5c - [Attributor] Teach AAPotentialValues about constant select conditions

[Johannes Doerfert via llvm-commits]

Author: Johannes Doerfert
Date: 2021-06-29T09:38:18-05:00
New Revision: 457bd5c8d52a110fac43d538a03e30ef49099974

URL: https://github.com/llvm/llvm-project/commit/457bd5c8d52a110fac43d538a03e30ef49099974
DIFF: https://github.com/llvm/llvm-project/commit/457bd5c8d52a110fac43d538a03e30ef49099974.diff

LOG: [Attributor] Teach AAPotentialValues about constant select conditions

There was a TODO but now we actually check if the select condition is
assumed constant and only look at the relevant operand.

Added: 
    

Modified: 
    llvm/lib/Transforms/IPO/AttributorAttributes.cpp
    llvm/test/Transforms/Attributor/value-simplify.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
index 25e0ff5599d4..5bcdf636ca1d 100644
--- a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -7823,23 +7823,46 @@ struct AAPotentialValuesFloating : AAPotentialValuesImpl {
     if (!LHS->getType()->isIntegerTy() || !RHS->getType()->isIntegerTy())
       return indicatePessimisticFixpoint();
 
-    // TODO: Use assumed simplified condition value
-    auto &LHSAA = A.getAAFor<AAPotentialValues>(*this, IRPosition::value(*LHS),
-                                                DepClassTy::REQUIRED);
-    if (!LHSAA.isValidState())
-      return indicatePessimisticFixpoint();
+    bool UsedAssumedInformation = false;
+    Optional<Constant *> C = A.getAssumedConstant(*SI->getCondition(), *this,
+                                                  UsedAssumedInformation);
+
+    // Check if we only need one operand.
+    bool OnlyLeft = false, OnlyRight = false;
+    if (C.hasValue() && *C && (*C)->isOneValue())
+      OnlyLeft = true;
+    else if (C.hasValue() && *C && (*C)->isZeroValue())
+      OnlyRight = true;
+
+    const AAPotentialValues *LHSAA = nullptr, *RHSAA = nullptr;
+    if (!OnlyRight) {
+      LHSAA = &A.getAAFor<AAPotentialValues>(*this, IRPosition::value(*LHS),
+                                             DepClassTy::REQUIRED);
+      if (!LHSAA->isValidState())
+        return indicatePessimisticFixpoint();
+    }
+    if (!OnlyLeft) {
+      RHSAA = &A.getAAFor<AAPotentialValues>(*this, IRPosition::value(*RHS),
+                                             DepClassTy::REQUIRED);
+      if (!RHSAA->isValidState())
+        return indicatePessimisticFixpoint();
+    }
 
-    auto &RHSAA = A.getAAFor<AAPotentialValues>(*this, IRPosition::value(*RHS),
-                                                DepClassTy::REQUIRED);
-    if (!RHSAA.isValidState())
-      return indicatePessimisticFixpoint();
+    if (!LHSAA || !RHSAA) {
+      // select (true/false), lhs, rhs
+      auto *OpAA = LHSAA ? LHSAA : RHSAA;
 
-    if (LHSAA.undefIsContained() && RHSAA.undefIsContained())
+      if (OpAA->undefIsContained())
+        unionAssumedWithUndef();
+      else
+        unionAssumed(*OpAA);
+
+    } else if (LHSAA->undefIsContained() && RHSAA->undefIsContained()) {
       // select i1 *, undef , undef => undef
       unionAssumedWithUndef();
-    else {
-      unionAssumed(LHSAA);
-      unionAssumed(RHSAA);
+    } else {
+      unionAssumed(*LHSAA);
+      unionAssumed(*RHSAA);
     }
     return AssumedBefore == getAssumed() ? ChangeStatus::UNCHANGED
                                          : ChangeStatus::CHANGED;

diff  --git a/llvm/test/Transforms/Attributor/value-simplify.ll b/llvm/test/Transforms/Attributor/value-simplify.ll
index db4b8b6ef88f..1d8b468e4313 100644
--- a/llvm/test/Transforms/Attributor/value-simplify.ll
+++ b/llvm/test/Transforms/Attributor/value-simplify.ll
@@ -1073,6 +1073,37 @@ b:
   ret i1 %cmp2
 }
 
+define i32 @test_select(i32 %c) {
+; IS__TUNIT____: Function Attrs: nofree nosync nounwind readnone willreturn
+; IS__TUNIT____-LABEL: define {{[^@]+}}@test_select
+; IS__TUNIT____-SAME: (i32 [[C:%.*]]) #[[ATTR1]] {
+; IS__TUNIT____-NEXT:    [[CALL:%.*]] = call i32 @select() #[[ATTR1]]
+; IS__TUNIT____-NEXT:    ret i32 [[CALL]]
+;
+; IS__CGSCC____: Function Attrs: nofree norecurse nosync nounwind readnone willreturn
+; IS__CGSCC____-LABEL: define {{[^@]+}}@test_select
+; IS__CGSCC____-SAME: (i32 [[C:%.*]]) #[[ATTR1]] {
+; IS__CGSCC____-NEXT:    ret i32 42
+;
+  %call = call i32 @select(i1 1, i32 42, i32 %c)
+  ret i32 %call
+}
+
+define internal i32 @select(i1 %a, i32 %b, i32 %c) {
+; IS__TUNIT____: Function Attrs: nofree nosync nounwind readnone willreturn
+; IS__TUNIT____-LABEL: define {{[^@]+}}@select
+; IS__TUNIT____-SAME: () #[[ATTR1]] {
+; IS__TUNIT____-NEXT:    ret i32 42
+;
+; IS__CGSCC____: Function Attrs: nofree norecurse nosync nounwind readnone willreturn
+; IS__CGSCC____-LABEL: define {{[^@]+}}@select
+; IS__CGSCC____-SAME: () #[[ATTR1]] {
+; IS__CGSCC____-NEXT:    ret i32 undef
+;
+  %s = select i1 %a, i32 %b, i32 %c
+  ret i32 %s
+}
+
 define i1 @icmp() {
 ; IS__TUNIT____: Function Attrs: nofree nosync nounwind readnone willreturn
 ; IS__TUNIT____-LABEL: define {{[^@]+}}@icmp