do_checks: do not set HpAlloc if the stack check fails

[ghc-hetmet.git] / compiler / codeGen / CgHeapery.lhs

diff --git a/compiler/codeGen/CgHeapery.lhs b/compiler/codeGen/CgHeapery.lhs
index 65f94d1..23d8852 100644 (file)
--- a/compiler/codeGen/CgHeapery.lhs
+++ b/compiler/codeGen/CgHeapery.lhs
@@ -443,22 +443,32 @@ do_checks' :: CmmExpr -> CmmExpr -> Bool -> Bool -> CmmStmts -> CmmExpr -> Code
 do_checks' stk_expr hp_expr stk_nonzero hp_nonzero reg_save_code rts_lbl
   = do { doGranAllocate hp_expr
 
-       -- Emit a block for the heap-check-failure code
-       ; blk_id <- forkLabelledCode $ do
-                       { whenC hp_nonzero $
-                               stmtC (CmmAssign (CmmGlobal HpAlloc) hp_expr)
+        -- The failure block: this saves the registers and jumps to
+        -- the appropriate RTS stub.
+        ; exit_blk_id <- forkLabelledCode $ do {
                        ; emitStmts reg_save_code
                        ; stmtC (CmmJump rts_lbl []) }
 
+       -- In the case of a heap-check failure, we must also set
+       -- HpAlloc.  NB. HpAlloc is *only* set if Hp has been
+       -- incremented by the heap check, it must not be set in the
+       -- event that a stack check failed, because the RTS stub will
+       -- retreat Hp by HpAlloc.
+       ; hp_blk_id <- if hp_nonzero
+                          then forkLabelledCode $ do
+                                 stmtC (CmmAssign (CmmGlobal HpAlloc) hp_expr)
+                                 stmtC (CmmBranch exit_blk_id)
+                          else return exit_blk_id
+
        -- Check for stack overflow *FIRST*; otherwise
        -- we might bumping Hp and then failing stack oflo
        ; whenC stk_nonzero
-               (stmtC (CmmCondBranch stk_oflo blk_id))
+               (stmtC (CmmCondBranch stk_oflo exit_blk_id))
 
        ; whenC hp_nonzero
                (stmtsC [CmmAssign hpReg 
                                (cmmOffsetExprB (CmmReg hpReg) hp_expr),
-                       CmmCondBranch hp_oflo blk_id]) 
+                       CmmCondBranch hp_oflo hp_blk_id])
                -- Bump heap pointer, and test for heap exhaustion
                -- Note that we don't move the heap pointer unless the 
                -- stack check succeeds.  Otherwise we might end up