[InstCombine] Fold extractvalue of phi

Just as we do for most other operations, we should push
extractvalue instructions through phis, if this does not increase
unfolded instruction count.

Author: nikic

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -1280,6 +1280,11 @@ Instruction *InstCombinerImpl::foldOpIntoPhi(Instruction &I, PHINode *PN) {
         InV = PN->getIncomingValue(i);
       NewPN->addIncoming(InV, PN->getIncomingBlock(i));
     }
+  } else if (auto *EV = dyn_cast<ExtractValueInst>(&I)) {
+    for (unsigned i = 0; i != NumPHIValues; ++i)
+      NewPN->addIncoming(Builder.CreateExtractValue(PN->getIncomingValue(i),
+                                                    EV->getIndices(), "phi.ev"),
+                         PN->getIncomingBlock(i));
   } else {
     CastInst *CI = cast<CastInst>(&I);
     Type *RetTy = CI->getType();
@@ -3399,6 +3404,10 @@ Instruction *InstCombinerImpl::visitExtractValueInst(ExtractValueInst &EV) {
     }
   }
 
+  if (auto *PN = dyn_cast<PHINode>(Agg))
+    if (Instruction *Res = foldOpIntoPhi(EV, PN))
+      return Res;
+
   // We could simplify extracts from other values. Note that nested extracts may
   // already be simplified implicitly by the above: extract (extract (insert) )
   // will be translated into extract ( insert ( extract ) ) first and then just

llvm/test/Transforms/InstCombine/phi-extractvalue.ll

@@ -393,9 +393,8 @@ define i32 @extractvalue_of_constant_phi(i1 %c) {
 ; CHECK:       else:
 ; CHECK-NEXT:    br label [[JOIN]]
 ; CHECK:       join:
-; CHECK-NEXT:    [[PHI:%.*]] = phi { i32, i32 } [ { i32 1, i32 2 }, [[IF]] ], [ { i32 3, i32 4 }, [[ELSE]] ]
-; CHECK-NEXT:    [[EV:%.*]] = extractvalue { i32, i32 } [[PHI]], 0
-; CHECK-NEXT:    ret i32 [[EV]]
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ 1, [[IF]] ], [ 3, [[ELSE]] ]
+; CHECK-NEXT:    ret i32 [[PHI]]
 ;
   br i1 %c, label %if, label %else
 
@@ -415,13 +414,13 @@ define i32 @extractvalue_of_one_constant_phi(i1 %c, { i32, i32 } %arg) {
 ; CHECK-LABEL: @extractvalue_of_one_constant_phi(
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
 ; CHECK:       if:
+; CHECK-NEXT:    [[PHI_EV:%.*]] = extractvalue { i32, i32 } [[ARG:%.*]], 0
 ; CHECK-NEXT:    br label [[JOIN:%.*]]
 ; CHECK:       else:
 ; CHECK-NEXT:    br label [[JOIN]]
 ; CHECK:       join:
-; CHECK-NEXT:    [[PHI:%.*]] = phi { i32, i32 } [ [[ARG:%.*]], [[IF]] ], [ { i32 3, i32 4 }, [[ELSE]] ]
-; CHECK-NEXT:    [[EV:%.*]] = extractvalue { i32, i32 } [[PHI]], 0
-; CHECK-NEXT:    ret i32 [[EV]]
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ [[PHI_EV]], [[IF]] ], [ 3, [[ELSE]] ]
+; CHECK-NEXT:    ret i32 [[PHI]]
 ;
   br i1 %c, label %if, label %else
 
@@ -445,9 +444,8 @@ define i32 @extractvalue_of_constant_phi_multi_index(i1 %c) {
 ; CHECK:       else:
 ; CHECK-NEXT:    br label [[JOIN]]
 ; CHECK:       join:
-; CHECK-NEXT:    [[PHI:%.*]] = phi { i32, { i32, i32 } } [ { i32 1, { i32, i32 } { i32 2, i32 3 } }, [[IF]] ], [ { i32 4, { i32, i32 } { i32 5, i32 6 } }, [[ELSE]] ]
-; CHECK-NEXT:    [[EV:%.*]] = extractvalue { i32, { i32, i32 } } [[PHI]], 1, 1
-; CHECK-NEXT:    ret i32 [[EV]]
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ 3, [[IF]] ], [ 6, [[ELSE]] ]
+; CHECK-NEXT:    ret i32 [[PHI]]
 ;
   br i1 %c, label %if, label %else
 
@@ -467,13 +465,13 @@ define i32 @extractvalue_of_one_constant_phi_multi_index(i1 %c, { i32, { i32, i3
 ; CHECK-LABEL: @extractvalue_of_one_constant_phi_multi_index(
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
 ; CHECK:       if:
+; CHECK-NEXT:    [[PHI_EV:%.*]] = extractvalue { i32, { i32, i32 } } [[ARG:%.*]], 1, 1
 ; CHECK-NEXT:    br label [[JOIN:%.*]]
 ; CHECK:       else:
 ; CHECK-NEXT:    br label [[JOIN]]
 ; CHECK:       join:
-; CHECK-NEXT:    [[PHI:%.*]] = phi { i32, { i32, i32 } } [ [[ARG:%.*]], [[IF]] ], [ { i32 4, { i32, i32 } { i32 5, i32 6 } }, [[ELSE]] ]
-; CHECK-NEXT:    [[EV:%.*]] = extractvalue { i32, { i32, i32 } } [[PHI]], 1, 1
-; CHECK-NEXT:    ret i32 [[EV]]
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ [[PHI_EV]], [[IF]] ], [ 6, [[ELSE]] ]
+; CHECK-NEXT:    ret i32 [[PHI]]
 ;
   br i1 %c, label %if, label %else