Emit ASM input in a constant context

Summary:
Some ASM input constraints (e.g., "i" and "n") require immediate values. At O0,
very few code transformations are performed. So if we cannot resolve to an
immediate when emitting the ASM input we shouldn't delay its processing.

Reviewers: rsmith, efriedma

Reviewed By: efriedma

Subscribers: rehana, efriedma, craig.topper, jyknight, cfe-commits

Differential Revision: https://reviews.llvm.org/D55616

llvm-svn: 349561

4 files changed, 26 insertions, 10 deletions

diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index 7b69cb097c8..269fad38b8d 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -685,7 +685,9 @@ bool TargetInfo::validateInputConstraint(
       // FIXME: Fail if % is used with the last operand.
       break;
     case 'i': // immediate integer.
+      break;
     case 'n': // immediate integer with a known value.
+      Info.setRequiresImmediate();
       break;
     case 'I':  // Various constant constraints with target-specific meanings.
     case 'J':
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index bc7a18af1e5..0242b48659d 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -1820,11 +1820,14 @@ llvm::Value* CodeGenFunction::EmitAsmInput(
   // If this can't be a register or memory, i.e., has to be a constant
   // (immediate or symbolic), try to emit it as such.
   if (!Info.allowsRegister() && !Info.allowsMemory()) {
+    if (Info.requiresImmediateConstant()) {
+      llvm::APSInt AsmConst = InputExpr->EvaluateKnownConstInt(getContext());
+      return llvm::ConstantInt::get(getLLVMContext(), AsmConst);
+    }
+
     Expr::EvalResult Result;
     if (InputExpr->EvaluateAsInt(Result, getContext()))
       return llvm::ConstantInt::get(getLLVMContext(), Result.Val.getInt());
-    assert(!Info.requiresImmediateConstant() &&
-           "Required-immediate inlineasm arg isn't constant?");
   }
 
   if (Info.allowsRegister() || !Info.allowsMemory())
diff --git a/clang/lib/Sema/SemaStmtAsm.cpp b/clang/lib/Sema/SemaStmtAsm.cpp
index d209266049e..b10b3d852c6 100644
--- a/clang/lib/Sema/SemaStmtAsm.cpp
+++ b/clang/lib/Sema/SemaStmtAsm.cpp
@@ -378,17 +378,17 @@ StmtResult Sema::ActOnGCCAsmStmt(SourceLocation AsmLoc, bool IsSimple,
                          << InputExpr->getSourceRange());
     } else if (Info.requiresImmediateConstant() && !Info.allowsRegister()) {
       if (!InputExpr->isValueDependent()) {
-        Expr::EvalResult EVResult;
-        if (!InputExpr->EvaluateAsInt(EVResult, Context))
+        llvm::SmallVector<PartialDiagnosticAt, 1> Diags;
+        llvm::APSInt Result = InputExpr->EvaluateKnownConstInt(Context, &Diags);
+        if (!Diags.empty())
           return StmtError(
               Diag(InputExpr->getBeginLoc(), diag::err_asm_immediate_expected)
               << Info.getConstraintStr() << InputExpr->getSourceRange());
-        llvm::APSInt Result = EVResult.Val.getInt();
-         if (!Info.isValidAsmImmediate(Result))
-           return StmtError(Diag(InputExpr->getBeginLoc(),
-                                 diag::err_invalid_asm_value_for_constraint)
-                            << Result.toString(10) << Info.getConstraintStr()
-                            << InputExpr->getSourceRange());
+        if (!Info.isValidAsmImmediate(Result))
+          return StmtError(Diag(InputExpr->getBeginLoc(),
+                                diag::err_invalid_asm_value_for_constraint)
+                           << Result.toString(10) << Info.getConstraintStr()
+                           << InputExpr->getSourceRange());
       }
 
     } else {
diff --git a/clang/test/CodeGen/builtin-constant-p.c b/clang/test/CodeGen/builtin-constant-p.c
index 7f4e7d07cc6..f1cd06ad4aa 100644
--- a/clang/test/CodeGen/builtin-constant-p.c
+++ b/clang/test/CodeGen/builtin-constant-p.c
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O2 | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O0 | FileCheck --check-prefix=O0 %s
 
 int a = 42;
 
@@ -166,3 +167,13 @@ struct { const char *t; int a; } test15[] = {
 
 extern char test16_v;
 struct { int a; } test16 = { __builtin_constant_p(test16_v) };
+
+extern unsigned long long test17_v;
+
+void test17() {
+  // O0: define void @test17
+  // O0: call void asm sideeffect "", {{.*}}(i32 -1) 
+  // CHECK: define void @test17
+  // CHECK: call void asm sideeffect "", {{.*}}(i32 -1) 
+  __asm__ __volatile__("" :: "n"( (__builtin_constant_p(test17_v) || 0) ? 1 : -1));
+}