Initial support for Win64 SEH IR emission

Description

Initial support for Win64 SEH IR emission

The lowering looks a lot like normal EH lowering, with the exception
that the exceptions are caught by executing filter expression code
instead of matching typeinfo globals. The filter expressions are
outlined into functions which are used in landingpad clauses where
typeinfo would normally go.

Major aspects that still need work:

  • Non-call exceptions in try bodies won't work yet. The plan is to outline the try block in the frontend to keep things simple.
  • Filter expressions cannot use local variables until capturing is implemented.
  • __finally blocks will not run after exceptions. Fixing this requires work in the LLVM SEH preparation pass.

The IR lowering looks like this:

// C code:
bool safe_div(int n, int d, int *r) {

__try {
  *r = normal_div(n, d);
} __except(_exception_code() == EXCEPTION_INT_DIVIDE_BY_ZERO) {
  return false;
}
return true;

}

; LLVM IR:
define i32 @filter(i8* %e, i8* %fp) {

%ehptrs = bitcast i8* %e to i32**
%ehrec = load i32** %ehptrs
%code = load i32* %ehrec
%matches = icmp eq i32 %code, i32 u0xC0000094
%matches.i32 = zext i1 %matches to i32
ret i32 %matches.i32

}

define i1 zeroext @safe_div(i32 %n, i32 %d, i32* %r) {

%rr = invoke i32 @normal_div(i32 %n, i32 %d)
    to label %normal unwind to label %lpad

normal:

store i32 %rr, i32* %r
ret i1 1

lpad:

%ehvals = landingpad {i8*, i32} personality i32 (...)* @__C_specific_handler
    catch i8* bitcast (i32 (i8*, i8*)* @filter to i8*)
%ehptr = extractvalue {i8*, i32} %ehvals, i32 0
%sel = extractvalue {i8*, i32} %ehvals, i32 1
%filter_sel = call i32 @llvm.eh.seh.typeid.for(i8* bitcast (i32 (i8*, i8*)* @filter to i8*))
%matches = icmp eq i32 %sel, %filter_sel
br i1 %matches, label %eh.except, label %eh.resume

eh.except:

ret i1 false

eh.resume:

resume

}

Reviewers: rjmccall, rsmith, majnemer

Differential Revision: http://reviews.llvm.org/D5607

Details

Committed
rnkJan 21 2015, 5:36 PM
Differential Revision
D5607: Initial SEH IR generation implementation
Parents
rL226759: Revert "Try to fix -Asserts build bots."
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