[clang] `__builtin_assume_aligned()` with constexpr argument crashes clang

[Artem-B]

Reproducer: https://godbolt.org/z/d6eeM34rd

float *words_;

constexpr int x(int a, int b) { return a+b; }

void *crash_me(int index) {
    return __builtin_assume_aligned(words_ + index, x(2,2));
}

Partial stack trace:

#4  0x00007fd5be232420 in __assert_fail_base (fmt=<optimized out>, assertion=<optimized out>, file=<optimized out>, line=578, function=<optimized out>) at ./assert/assert.c:118
#5  0x00007fd5c7fd0914 in llvm::cast<llvm::ConstantInt, llvm::Value> (Val=0x556d3e9886d0) at /usr/local/google/home/tra/work/llvm/repo/llvm/include/llvm/Support/Casting.h:578
#6  0x00007fd5c801592c in clang::CodeGen::CodeGenFunction::EmitBuiltinExpr (this=0x7ffe61027380, GD=..., BuiltinID=202, E=0x556d3e964d48, ReturnValue=...) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGBuiltin.cpp:3543
#7  0x00007fd5c83429ac in clang::CodeGen::CodeGenFunction::EmitCallExpr (this=0x7ffe61027380, E=0x556d3e964d48, ReturnValue=..., CallOrInvoke=0x7ffe61025a40) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExpr.cpp:5962
#8  0x00007fd5c83f4de1 in (anonymous namespace)::ScalarExprEmitter::VisitCallExpr (this=0x7ffe61025c60, E=0x556d3e964d48) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:631
#9  0x00007fd5c83eb9e1 in clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit (this=0x7ffe61025c60, S=0x556d3e964d48) at tools/clang/include/clang/AST/StmtNodes.inc:608
#10 0x00007fd5c83e1225 in (anonymous namespace)::ScalarExprEmitter::Visit (this=0x7ffe61025c60, E=0x556d3e964d48) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:452
#11 0x00007fd5c83e1062 in clang::CodeGen::CodeGenFunction::EmitScalarExpr (this=0x7ffe61027380, E=0x556d3e964d48, IgnoreResultAssign=false) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:5873
#12 0x00007fd5c86494b5 in clang::CodeGen::CodeGenFunction::EmitReturnStmt (this=0x7ffe61027380, S=...) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGStmt.cpp:1692

Root cause is the implicit assumption in CGBuiltin.cpp

llvm-project/clang/lib/CodeGen/CGBuiltin.cpp

Lines 3540 to 3543 in b629981

	(E->getNumArgs() > 2) ? EmitScalarExpr(E->getArg(2)) : nullptr;
	Value *AlignmentValue = EmitScalarExpr(E->getArg(1));
	ConstantInt *AlignmentCI = cast<ConstantInt>(AlignmentValue);

Instead of the hard cast of the emitted argument, the code should've evaluated the argument value and used it instead. Sema already verifies that we can evaluate the argument value.

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Artem Belevich (Artem-B)

Reproducer: https://godbolt.org/z/d6eeM34rd

float *words_;

constexpr int x(int a, int b) { return a+b; }

void *crash_me(int index) {
    return __builtin_assume_aligned(words_ + index, x(2,2));
}

Partial stack trace:

#<!-- -->4  0x00007fd5be232420 in __assert_fail_base (fmt=&lt;optimized out&gt;, assertion=&lt;optimized out&gt;, file=&lt;optimized out&gt;, line=578, function=&lt;optimized out&gt;) at ./assert/assert.c:118
#<!-- -->5  0x00007fd5c7fd0914 in llvm::cast&lt;llvm::ConstantInt, llvm::Value&gt; (Val=0x556d3e9886d0) at /usr/local/google/home/tra/work/llvm/repo/llvm/include/llvm/Support/Casting.h:578
#<!-- -->6  0x00007fd5c801592c in clang::CodeGen::CodeGenFunction::EmitBuiltinExpr (this=0x7ffe61027380, GD=..., BuiltinID=202, E=0x556d3e964d48, ReturnValue=...) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGBuiltin.cpp:3543
#<!-- -->7  0x00007fd5c83429ac in clang::CodeGen::CodeGenFunction::EmitCallExpr (this=0x7ffe61027380, E=0x556d3e964d48, ReturnValue=..., CallOrInvoke=0x7ffe61025a40) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExpr.cpp:5962
#<!-- -->8  0x00007fd5c83f4de1 in (anonymous namespace)::ScalarExprEmitter::VisitCallExpr (this=0x7ffe61025c60, E=0x556d3e964d48) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:631
#<!-- -->9  0x00007fd5c83eb9e1 in clang::StmtVisitorBase&lt;std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*&gt;::Visit (this=0x7ffe61025c60, S=0x556d3e964d48) at tools/clang/include/clang/AST/StmtNodes.inc:608
#<!-- -->10 0x00007fd5c83e1225 in (anonymous namespace)::ScalarExprEmitter::Visit (this=0x7ffe61025c60, E=0x556d3e964d48) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:452
#<!-- -->11 0x00007fd5c83e1062 in clang::CodeGen::CodeGenFunction::EmitScalarExpr (this=0x7ffe61027380, E=0x556d3e964d48, IgnoreResultAssign=false) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:5873
#<!-- -->12 0x00007fd5c86494b5 in clang::CodeGen::CodeGenFunction::EmitReturnStmt (this=0x7ffe61027380, S=...) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGStmt.cpp:1692

Root cause is the implicit assumption in CGBuiltin.cpp

llvm-project/clang/lib/CodeGen/CGBuiltin.cpp

Lines 3540 to 3543 in b629981

	(E->getNumArgs() > 2) ? EmitScalarExpr(E->getArg(2)) : nullptr;
	Value *AlignmentValue = EmitScalarExpr(E->getArg(1));
	ConstantInt *AlignmentCI = cast<ConstantInt>(AlignmentValue);

Instead of the hard cast of the emitted argument, the code should've evaluated the argument value and used it instead. Sema already verifies that we can evaluate the argument value.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Artem Belevich (Artem-B)

Reproducer: https://godbolt.org/z/d6eeM34rd

float *words_;

constexpr int x(int a, int b) { return a+b; }

void *crash_me(int index) {
    return __builtin_assume_aligned(words_ + index, x(2,2));
}

Partial stack trace:

#<!-- -->4  0x00007fd5be232420 in __assert_fail_base (fmt=&lt;optimized out&gt;, assertion=&lt;optimized out&gt;, file=&lt;optimized out&gt;, line=578, function=&lt;optimized out&gt;) at ./assert/assert.c:118
#<!-- -->5  0x00007fd5c7fd0914 in llvm::cast&lt;llvm::ConstantInt, llvm::Value&gt; (Val=0x556d3e9886d0) at /usr/local/google/home/tra/work/llvm/repo/llvm/include/llvm/Support/Casting.h:578
#<!-- -->6  0x00007fd5c801592c in clang::CodeGen::CodeGenFunction::EmitBuiltinExpr (this=0x7ffe61027380, GD=..., BuiltinID=202, E=0x556d3e964d48, ReturnValue=...) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGBuiltin.cpp:3543
#<!-- -->7  0x00007fd5c83429ac in clang::CodeGen::CodeGenFunction::EmitCallExpr (this=0x7ffe61027380, E=0x556d3e964d48, ReturnValue=..., CallOrInvoke=0x7ffe61025a40) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExpr.cpp:5962
#<!-- -->8  0x00007fd5c83f4de1 in (anonymous namespace)::ScalarExprEmitter::VisitCallExpr (this=0x7ffe61025c60, E=0x556d3e964d48) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:631
#<!-- -->9  0x00007fd5c83eb9e1 in clang::StmtVisitorBase&lt;std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*&gt;::Visit (this=0x7ffe61025c60, S=0x556d3e964d48) at tools/clang/include/clang/AST/StmtNodes.inc:608
#<!-- -->10 0x00007fd5c83e1225 in (anonymous namespace)::ScalarExprEmitter::Visit (this=0x7ffe61025c60, E=0x556d3e964d48) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:452
#<!-- -->11 0x00007fd5c83e1062 in clang::CodeGen::CodeGenFunction::EmitScalarExpr (this=0x7ffe61027380, E=0x556d3e964d48, IgnoreResultAssign=false) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGExprScalar.cpp:5873
#<!-- -->12 0x00007fd5c86494b5 in clang::CodeGen::CodeGenFunction::EmitReturnStmt (this=0x7ffe61027380, S=...) at /usr/local/google/home/tra/work/llvm/repo/clang/lib/CodeGen/CGStmt.cpp:1692

Root cause is the implicit assumption in CGBuiltin.cpp

llvm-project/clang/lib/CodeGen/CGBuiltin.cpp

Lines 3540 to 3543 in b629981

	(E->getNumArgs() > 2) ? EmitScalarExpr(E->getArg(2)) : nullptr;
	Value *AlignmentValue = EmitScalarExpr(E->getArg(1));
	ConstantInt *AlignmentCI = cast<ConstantInt>(AlignmentValue);

Instead of the hard cast of the emitted argument, the code should've evaluated the argument value and used it instead. Sema already verifies that we can evaluate the argument value.