llvm-reduce: Skip setting br conditions on already constant branches

llvm/test/tools/llvm-reduce/simplify-conditionals-already-constant-brcond.ll

@@ -0,0 +1,139 @@
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=simplify-conditionals-false --test FileCheck --test-arg --check-prefixes=INTERESTING --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck -check-prefixes=RESULT-FALSE,CHECK %s < %t
+
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=simplify-conditionals-true --test FileCheck --test-arg --check-prefixes=INTERESTING --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck -check-prefixes=RESULT-TRUE,CHECK %s < %t
+
+; Check that simplify-conditionals-true/false do not attempt block
+; simplification in cases that happened to already use a constant
+; true/false branch. We should not get the side effect of running
+; simplifycfg on blocks where we did not change the terminator value,
+; and not introduce unreachable code.
+
+
+; CHECK-LABEL: @br_false(
+; RESULT-FALSE: br i1 false, label %will_be_unreachable, label %exit
+; RESULT-TRUE: br label %will_be_unreachable
+define i1 @br_false(i64 %int) {
+entry:
+  %i2p = inttoptr i64 %int to ptr
+  br i1 false, label %will_be_unreachable, label %exit
+
+will_be_unreachable:
+  %load = load ptr, ptr %i2p, align 8
+  br label %for.body
+
+for.body:
+  br label %for.body
+
+exit:
+  ret i1 false
+}
+
+; CHECK-LABEL: @br_false_keep_in_unreachable(
+; CHECK: entry
+; INTERESTING: [[I2P:%.+]] = inttoptr i64 %int to ptr
+; INTERESTING: load ptr, ptr [[I2P]]
+
+; RESULT-FALSE: br i1 false, label %will_be_unreachable, label %exit
+; RESULT-TRUE: br label %will_be_unreachable
+define i1 @br_false_keep_in_unreachable(i64 %int) {
+entry:
+  br i1 false, label %will_be_unreachable, label %exit
+
+will_be_unreachable:
+  %i2p = inttoptr i64 %int to ptr
+  %load = load ptr, ptr %i2p, align 8
+  br label %for.body
+
+for.body:
+  br label %for.body
+
+exit:
+  ret i1 false
+}
+
+; CHECK-LABEL: @br_true(
+
+; RESULT-FALSE: br label %will_be_unreachable
+; RESULT-TRUE: br i1 true, label %exit, label %will_be_unreachable
+define i1 @br_true(i64 %int) {
+entry:
+  %i2p = inttoptr i64 %int to ptr
+  br i1 true, label %exit, label %will_be_unreachable
+
+will_be_unreachable:
+  %load = load ptr, ptr %i2p, align 8
+  br label %for.body
+
+for.body:
+  br label %for.body
+
+exit:
+  ret i1 false
+}
+
+; CHECK-LABEL: @br_true_keep_in_unreachable(
+; CHECK: entry:
+; INTERESTING: [[I2P:%.+]] = inttoptr i64 %int to ptr
+; INTERESTING: load ptr, ptr [[I2P]]
+
+; RESULT-FALSE: br label %will_be_unreachable
+; RESULT-TRUE: br i1 true, label %exit, label %will_be_unreachable
+define i1 @br_true_keep_in_unreachable(i64 %int) {
+entry:
+  %i2p = inttoptr i64 %int to ptr
+  br i1 true, label %exit, label %will_be_unreachable
+
+will_be_unreachable:
+  %load = load ptr, ptr %i2p, align 8
+  br label %for.body
+
+for.body:
+  br label %for.body
+
+exit:
+  ret i1 false
+}
+
+; CHECK-LABEL: @br_poison(
+; RESULT-FALSE: br label %will_be_unreachable
+; RESULT-TRUE: br label %exit
+define i1 @br_poison(i64 %int) {
+entry:
+  %i2p = inttoptr i64 %int to ptr
+  br i1 poison, label %exit, label %will_be_unreachable
+
+will_be_unreachable:
+  %load = load ptr, ptr %i2p, align 8
+  br label %for.body
+
+for.body:
+  br label %for.body
+
+exit:
+  ret i1 false
+}
+
+; CHECK-LABEL: @br_poison_keep_in_unreachable(
+; CHECK: entry:
+; INTERESTING: [[I2P:%.+]] = inttoptr i64 %int to ptr
+; INTERESTING: load ptr, ptr [[I2P]]
+
+; RESULT-FALSE: br label %will_be_unreachable
+; RESULT-TRUE: br label %exit
+define i1 @br_poison_keep_in_unreachable(i64 %int) {
+entry:
+  %i2p = inttoptr i64 %int to ptr
+  br i1 poison, label %exit, label %will_be_unreachable
+
+will_be_unreachable:
+  %load = load ptr, ptr %i2p, align 8
+  br label %for.body
+
+for.body:
+  br label %for.body
+
+exit:
+  ret i1 false
+}

llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp

@@ -37,17 +37,18 @@ static void reduceConditionals(Oracle &O, ReducerWorkItem &WorkItem,
   Module &M = WorkItem.getModule();
   SmallVector<BasicBlock *, 16> ToSimplify;
 
+  LLVMContext &Ctx = M.getContext();
+  ConstantInt *ConstValToSet =
+      Direction ? ConstantInt::getTrue(Ctx) : ConstantInt::getFalse(Ctx);
+
   for (auto &F : M) {
     for (auto &BB : F) {
       auto *BR = dyn_cast<BranchInst>(BB.getTerminator());
-      if (!BR || !BR->isConditional() || O.shouldKeep())
+      if (!BR || !BR->isConditional() || BR->getCondition() == ConstValToSet ||
+          O.shouldKeep())
         continue;
 
-      if (Direction)
-        BR->setCondition(ConstantInt::getTrue(BR->getContext()));
-      else
-        BR->setCondition(ConstantInt::getFalse(BR->getContext()));
-
+      BR->setCondition(ConstValToSet);
       ToSimplify.push_back(&BB);
     }
   }